An analytical model to predict the thermal performance of a novel parallel flow packed bed solar air heater

A design of a parallel flow solar air heater with packed material in its upper channel and capable of providing a higher heat flux compared to the conventional non-porous bed double flow systems is presented. An analytical model describing the various temperatures and heat transfer characteristics of such a parallel flow packed bed solar air heater (PFPBSAH) has been developed and employed to study the effects of the mass flow rate and varying porosities of the packed material on its thermal performance. The model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass exchanges involved. To validate the proposed analytical model, comparisons between theoretical and experimental results showed that good agreement is achieved with reasonable accuracy. Also, PFPBSAH is found to perform more efficiently than the conventional non-porous double flow solar air heaters with 10–20% increase in its thermal efficiency. Furthermore, the effect of the fraction of mass flow rate in the upper or lower flow channel of PFPBSAH device on its performance, has also investigated theoretically. The fraction of the mass flow rate in the respective channels of the PFPBSAH is shown to be dominant parameter in determining the effective thermal efficiency of the heater.     

The Effect of Colour Contrast on Consumers' Attentive Behaviours and Perception of Fresh Produce

The market for fruits and vegetables has received considerable interest in recent years, with much of its growth attributed to consumer interest in nutrition and health. Quality has been indicated to be the most important factor in produce sales, and appearance is of noted significance with regard to perceived quality. The broad objectives of this research were to identify the impact of simultaneous colour contrast (i.e. the produce viewed through a mesh bag) on (a) attentive behaviours as measured by eye tracking and (b) perceived quality, visual appeal and purchase intention as measured with a Likert scale. To accomplish these objectives, six different types of produce (red apples, oranges, lemons, green apples, purple onions and white onions) were photographed with four differently coloured mesh treatments: the same (as the produce), complementary, complementary‐analogous and analogous. Visual stimuli were then presented during the eye tracking study and in a subsequent questionnaire. Colour contrast was found to have a significant effect on both resultant eye tracking variables [number of visual fixations (p < 0.001) and time spent (p < 0.001)]. Produce shown with mesh of the same, or an analogous colour, induced significantly more visual fixations and more time than those depicted with complementary or complementary‐analogous treatments. Subsequent to the eye tracking study, subjects were shown the stimuli and asked to rate the expected quality, visual appeal and their purchase intention for the 24 photographs (6 types of produce × 4 colour contrasts) by using a Likert scale. Pairwise comparisons suggested that produce packaged in the same or analogous mesh were perceived by subjects to be of higher quality, more visually appealing and evoked a higher level of purchase intention than those packaged in complementary or complementary‐analogous mesh (α = 0.05). Copyright © 2012 John Wiley & Sons, Ltd.     

Nanoscale Flexoelectricity

Electromechanical effects are ubiquitous in biological and materials systems. Understanding the fundamentals of these coupling phenomena is critical to devising next‐generation electromechanical transducers. Piezoelectricity has been studied in detail, in both the bulk and at mesoscopic scales. Recently, an increasing amount of attention has been paid to flexoelectricity: electrical polarization induced by a strain gradient. While piezoelectricity requires crystalline structures with no inversion symmetry, flexoelectricity does not carry this requirement, since the effect is caused by inhomogeneous strains. Flexoelectricity explains many interesting electromechanical behaviors in hard crystalline materials and underpins core mechanoelectric transduction phenomena in soft biomaterials. Most excitingly, flexoelectricity is a size‐dependent effect which becomes more significant in nanoscale systems. With increasing interest in nanoscale and nano‐bio hybrid materials, flexoelectricity will continue to gain prominence. This Review summarizes work in this area. First, methods to amplify or manipulate the flexoelectric effect to enhance material properties will be investigated, particularly at nanometer scales. Next, the nature and history of these effects in soft biomaterials will be explored. Finally, some theoretical interpretations for the effect will be presented. Overall, flexoelectricity represents an exciting phenomenon which is expected to become more considerable as materials continue to shrink.     

Ferroelasticity in a metal–organic framework perovskite; towards a new class of multiferroics

A metal–organic framework perovskite, [(CH₂)₃NH₂][Mn(HCOO)₃], exhibits a weakly first order ferroelastic phase transition at ～272 K, from orthorhombic Pnma to monoclinic P2₁/n, and a further transition associated with antiferromagnetic ordering at ～8.5 K. The main structural changes, through the phase transition, are orientational ordering of the azetidium groups and associated changes in hydrogen bonding. In marked contrast to conventional improper ferroelastic oxide perovskites, the driving mechanism is associated with the X-point of the cubic Brillouin zone rather than being driven by R- and M-point octahedral tilting. The total ferroelastic shear strain of up to ～5% is substantially greater than found for typical oxide perovskites, and highlights the potential of the flexible framework to undergo large relaxations in response to local structural changes. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show some of the characteristic features of ferroelastic materials. In particular, acoustic dissipation below the transition point can be understood in terms of mobility of twin walls under the influence of external stress with relaxation times on the order of ～10^?7 s. Elastic softening as the transition is approached from above is interpreted in terms of coupling between acoustic modes and dynamic local ordering of the azetidium groups. Subsequent stiffening with further temperature reduction is interpreted in terms of classical strain–order parameter coupling at an improper ferroelastic transition which is close to being tricritical. By way of contrast, there are no overt changes in elastic or anelastic properties near 9 K, implying that any coupling of the antiferromagnetic order parameter with strain is weak or negligible.     

Selective deposition of catalyst nanoparticles using the gravitational force for carbon nanotubes interconnect

The photolithography process has generally been used for the making of catalyst layers used for the synthesis of CNTs due to its comparative ease. However, this method results in the formation of undesirable catalyst particles, which deteriorate the quality of the devices. Therefore, we tried to form a catalyst layer without using any lift-off or wet etching process, especially for the formation of carbon nanotube interconnects. After spin coating the samples, which were previously fabricated with several vias, with an iron-acetate solution, the catalyst layer was pulled down into the bottom of the holes through the force of gravity. We were able to remove the catalyst layer which was coated over undesirable areas, by TMAH (tetramethylammonium hydroxide, N(CH₃)₄OH) treatment. After the catalyst deposition process, we synthesized CNTs and observed them by scanning electron microscopy (SEM).     

Streptococcus thermophilus strains of plant origin as dairy starters: Isolation and characterisation

Streptococcus thermophilus strains have been isolated mainly from dairy environments. To prospect for new strains of S. thermophilus, isolation was made from different plant sources. In this study, 74 plant isolates were characterised as S. thermophilus by a polyphasic approach and by 16S rRNA sequencing. The isolates were further evaluated for their physiological and biochemical properties. Plant isolates exhibited good acid production and varying proteolytic activity. All the isolates showed acetaldehyde and capsular exopolysaccharide (EPS) production and few revealed diacetyl production. In contrast to industrial strains, six isolates were able to ferment galactose and 25 were found to have no urease activity. Both the plant isolates and reference dairy cultures were found to possess similar physiological and biochemical properties and can be considered for developing new starters.     

Localized surface plasmon resonances arising from free carriers in doped quantum dots

Localized surface plasmon resonances (LSPRs) typically arise in nanostructures of noble metals resulting in enhanced and geometrically tunable absorption and scattering resonances. LSPRs, however, are not limited to nanostructures of metals and can also be achieved in semiconductor nanocrystals with appreciable free carrier concentrations. Here, we describe well-defined LSPRs arising from p-type carriers in vacancy-doped semiconductor quantum dots (QDs). Achievement of LSPRs by free carrier doping of a semiconductor nanocrystal would allow active on-chip control of LSPR responses. Plasmonic sensing and manipulation of solid-state processes in single nanocrystals constitutes another interesting possibility. We also demonstrate that doped semiconductor QDs allow realization of LSPRs and quantum-confined excitons within the same nanostructure, opening up the possibility of strong coupling of photonic and electronic modes, with implications for light harvesting, nonlinear optics, and quantum information processing.     

Synthesis of hydrophilic superparamagnetic magnetite nanoparticles via thermal decomposition of Fe(acac), in 80 vol% TREG + 20 vol% TREM

In this paper, we report single step synthesis of hydrophilic superparamagnetic magnetite nanoparticles by thermolysis of Fe(acac)3 and their characterization of the properties relevant to biomedical applications like hyperthermia and magnetic resonance imaging (MRI). Size and morphology of the particles were determined by Transmission electron microscopy (TEM) while phase purity and structure of the particles were identified by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Magnetic properties were evaluated using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID) measurements. The as prepared nanoparticles were found to be superparamagnetic with the blocking temperature of 136 K and were easily suspendable in water. Cytotoxicity studies on human cervical (SiHa), mouse melanoma (B16F10) and mouse primary fibroblast cells demonstrated that up to a dose of 0.1 mg/ml, the magnetite nanoparticles were nontoxic to the cells. To evaluate the feasibility of their uses in hyperthermia and MRI applications, specific absorption rate (SAR) and spin-spin relaxation time (T2) were measured respectively. SAR has been calculated to be above 80 Watt/g for samples with the iron concentration of 5-20 mg/ml at 10 kA/m AC magnetic field and 425 kHz frequency. r2 relaxivity value was measured as 358.4 mM(-1)S(-1) which is almost double as compared to that of the Resovist, a commercially available MRI contrast agent. Thus the as-prepared magnetite nanoparticles may be used for hyperthermia and MRI applications due to their promising SAR and r2 values.     

Amorphous silicon–carbon based nano-scale thin film anode materials for lithium ion batteries

The buffering effect of carbon on the structural stability of amorphous silicon films, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin film (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin films, denoted as a-C/Si, has been investigated. In comparison to pure amorphous Si thin film (a-Si) which shows a rapid fade in capacity after 30 cycles, the a-C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 μA/cm² (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a-Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a-Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a-C/Si thin film during the alloying/dealloying process with lithium has been confirmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin film battery systems.