A calibrated UV-LED based light source for water purification and characterisation of photocatalysis.

Photocatalysis has a potential to become a cost effective industrial process for water cleaning. One of the most studied photocatalysts is titanium dioxide which, as a wide band gap semiconductor, requires ultraviolet (UV) light for its photoactivation. This is at the wavelengths where the efficiency of present-day light emitting diodes (LEDs) decreases rapidly, which presents a challenge in the use of UV-LEDs for commercially viable photocatalysis. There is also a need for accurate photocatalysis measurement of remediation rates of water-borne contaminants for determining optimum exposure doses in industrial applications. In response to these challenges, this paper describes a UV-LED based photocatalytic test reactor that provides a calibrated adjustable light source and pre-defined test conditions to remove as many sources of uncertainty in photocatalytic analysis as possible and thereby improve data reliability. The test reactor provides a selectable intensity of up to 1.9 kW m-2 at the photocatalyst surface. The comparability of the results is achieved through the use of pre-calibration and control electronics that minimize the largest sources of uncertainty; most notably variations in the intensity and directionality of the UV light emission of LEDs and in LED device heating.

Prediction of Short-Distance Aerial Movement of Phakopsora pachyrhizi Urediniospores Using Machine Learning.

Dispersal of urediniospores by wind is the primary means of spread for Phakopsora pachyrhizi, the cause of soybean rust. Our research focused on the short-distance movement of urediniospores from within the soybean canopy and up to 61 m from field-grown rust-infected soybean plants. Environmental variables were used to develop and compare models including the least absolute shrinkage and selection operator regression, zero-inflated Poisson/regular Poisson regression, random forest, and neural network to describe deposition of urediniospores collected in passive and active traps. All four models identified distance of trap from source, humidity, temperature, wind direction, and wind speed as the five most important variables influencing short-distance movement of urediniospores. The random forest model provided the best predictions, explaining 76.1 and 86.8% of the total variation in the passive- and active-trap datasets, respectively. The prediction accuracy based on the correlation coefficient (r) between predicted values and the true values were 0.83 (P < 0.0001) and 0.94 (P < 0.0001) for the passive and active trap datasets, respectively. Overall, multiple machine learning techniques identified the most important variables to make the most accurate predictions of movement of P. pachyrhizi urediniospores short-distance.

Effect of Fungicide Application and Cultivar on Soybean Green Stem Disorder.

Green stem disorder of soybean (Glycine max) has increasingly become a nuisance for soybean producers. The disorder is distinguished from other manifestations of delayed plant maturity by the delayed senescence of stems only, with normal pod ripening and seed maturation. The primary objective of the first study was to determine whether green stem disorder increased with a fungicide treatment. Field cages to isolate soybean plants to prevent insect interactions were used and treatments included maturity group (MG) II insensitive and sensitive soybean cultivars with or without fungicide applications. A secondary objective was to determine fungi potentially associated with the disorder. The results indicated significant elevation of the incidence of green stem disorder when using a fungicide. Species of Diaporthe or Phomopsis and Macrophomina phaseolina were more frequent in stems without the disorder, whereas species of Colletotrichum were found mostly in stems with the disorder. In another study, field experiments were conducted without cages in replicated field plots to compare the effects of fungicides with different chemistries and timing of fungicide application on incidence of green stem disorder using green stem disorder MG II- and MG III-sensitive and insensitive soybean cultivars. There was a significant increase in percentage of green stem disorder due to fungicide application, depending on fungicide chemistry, timing of application, year, location, and cultivar sensitivity to green stem disorder. Generally, Headline and Headline-Domark applications resulted in higher incidence of green stem disorder than Domark alone or the nonsprayed control, with over 50% incidence in many cases. Higher percent green stem disorder was significantly (P < 0.05) associated with higher yields in 11 of the 28 trials. From the results of this research, soybean producers should be aware of the possible risk that fungicide application may have in increasing incidence of green stem disorder. In addition, producers can help manage green stem disorder by selecting soybean cultivars reported to be consistently insensitive to the disorder.

Angle dependent optical properties of polymer films with a biomimetic anti-reflecting surface replicated from cylindrical and tapered nanoporous alumina.

Anodic porous alumina nanostructures have been fabricated with tapered and cylindrical pores with a spacing of 100 and 200 nm and depth of 180-500 nm. The porous nanostructures were replicated into polymer films to create a moth-eye anti-reflecting surface by a roll-to-roll UV replication process. The angle dependent optical transmission of the resulting polymer films exhibited up to a 2% increase in transmission at a normal angle and up to a 5% increase in transmission at a 70° angle of incidence to an equivalent film with a surface replicated from polished aluminum. No significant difference was observed between the optical performance of moth-eye surfaces formed from cylindrical and tapered nano-pores.

Multi-Year Evaluation of Commercial Soybean Cultivars for Resistance to Phytophthora sojae.

Phytophthora sojae causes damping-off, root rot, and stem rot of soybean, particularly in poorly drained soils. Soybean cultivar resistance is one of the primary methods to control this disease, with Rps1c, Rps1k, and Rps1a being the most commonly used genes. The Varietal Information Program for Soybeans (VIPS) at the University of Illinois evaluates soybean cultivars for resistance to a number of diseases including Phytophthora root rot (PRR). The objectives of this research were to evaluate PRR resistance among commercial cultivars or advanced lines, and to compare these results with the information on PRR resistance provided by the company that entered the cultivar in VIPS. Each year from 2004 to 2008, between 600 and 900 cultivars were evaluated for resistance to either race 17 or 26 of P. sojae using the hypocotyl inoculation method. P. sojae single resistance genes were reported in 1,808 or 51% of the entries based on company information. Of these, the most commonly reported resistance genes were Rps1c (50%), Rps1k (40%), and Rps1a (10%). To a much smaller degree, companies reported using Rps3a (0.3%), Rps1b (0.2%), and Rps7 (0.2%). For the duration of the 5-year testing period, almost half of the cultivars (46%) were entered in VIPS with no reported resistance genes, and only nine out of a total of 3,533 entries (less than 0.3%) reported a stacked combination of resistance genes. Agreement between company-reported genes and any resistance found in the VIPS PRR evaluation was highest for those cultivars claiming to have Rps1c (90%) and Rps1k (83%), followed by Rps1a (70%). On average, 54% of the cultivars submitted to VIPS each year were new, reflecting the rapid development and turnover of soybean cultivars provided by the soybean seed companies.

Anodised titania nanotubes prepared in a glycerol/NaF electrolyte.

This paper discusses the preparation of titania nanotubes by anodisation of Ti in a glycerol-based electrolyte containing 0.5% wt of sodium fluoride (NaF). The influence of anodisation voltage and anodisation time on nanotube wall thickness, diameter and length has been investigated. The results indicate that nanotubes can be formed within a voltage range 10-40 V and that the tubular structure is lost when using a higher voltage. The diameter of the nanotubes is voltage dependent, with the widest tubes being obtained at the highest possible applied voltage of 40 V. An initial voltage ramp which increases at 100 mV/s to the anodisation voltage, rather than an instantaneous step, was observed to stabilise the metal-oxide interface. This enabled the growth of anodic films up to 5.5 microm in length by anodising for approximately 48 h. In the absence of a voltage ramp the films tended to collapse and become detached from the titanium electrode after 15-20 h. Electron microscopy observation suggests that the nanotubes in glycerol develop in a similar way to those produced in water-based media. The nanotubes formed using glycerol also exhibit ripples along the tube wall, although, growing at a slower rate, they are generally smoother than those formed in water.

Experimental analysis of the dynamical response of energy harvesting devices based on bistable laminated plates.

The use of bistable laminates is a potential approach to realize broadband piezoelectric based energy harvesting systems. In this paper the dynamic response of a piezoelectric material attached to a bistable laminate plate is examined based on the experimental generated voltage time series. The system was subjected to harmonic excitations and exhibited single-well and snap-through vibrations of both periodic and chaotic character. To identify the dynamics of the system response we examined the frequency spectrum, bifurcation diagrams, phase portraits, and the 0-1 test.

Polarization of porous hydroxyapatite scaffolds: influence on osteoblast cell proliferation and extracellular matrix production.

Improvements to clinically used biomaterials such as hydroxyapatite (HA) are of potential benefit to the patient. One modification, the addition of surface charges, has been shown to have an important role influencing cell response. In this study, porous HA scaffolds with both positive and negative surface charges were manufactured. The samples were sintered in air to produce porous HA ceramic scaffolds in the form of cylinders 12 mm in height × 7 mm in diameter. These were polarized with a dc voltage of 3 kV/cm. MC3T3E1 cells were placed on either negative or positive ends of the charged (or unpoled control) HA scaffolds. At 7 days, picogreen analysis was performed to analyze the cell number at the negative (4 mm), central (4 mm), and positive (4 mm) portions of the 12 mm cylindrical scaffold. At 4 weeks, micro-CT analysis was performed to quantify the regional volume of mineralized matrix deposition on the 3D scaffold. At 7 days, there were significantly more cells present at the negative end of the scaffold when seeded from the negative end in comparison to the other samples tested. Micro-CT data at 4 weeks correlated with this finding, demonstrating an increase in mineralized matrix at the negatively charged end of the scaffold seeded from the negative end in comparison to the positively charged and unpoled control scaffolds. The results indicate that the charge on HA influences cell activity and that this phenomenon can be translated to a clinically relevant porous scaffold structure.

Modification of standard CMOS technology for cell-based biosensors.

We present an electrode based on complementary metal oxide semiconductor (CMOS) technology that can be made fully biocompatible and chemically inert using a simple, low-cost and non-specialised process. Since these devices are based on ubiquitous CMOS technology, the integrated circuits can be readily developed to include appropriate amplifiers, filters and wireless subsystems, thus reducing the complexity and cost of external systems. The unprocessed CMOS aluminium electrodes are modified using anodisation and plating techniques which do not require intricate and expensive semiconductor processing equipment and can be performed on the bench-top as a clean-room environment is not required. The resulting transducers are able to detect both the fast electrical activity of neurons and the slow changes in impedance of growing and dividing cells. By using standard semiconductor fabrication techniques and well-established technologies, the approach can form the basis of cell-based biosensors and transducers for high throughput drug discovery assays, neuroprosthetics and as a basic research tool in biosciences. The technology is equally applicable to other biosensors that require noble metal or nanoporous microelectrodes.

Electrically active bioceramics: a review of interfacial responses.

Electrical potentials in mechanically loaded bone have been implicated as signals in the bone remodeling cycle. Recently, interest has grown in exploiting this phenomenon to develop electrically active ceramics for implantation in hard tissue which may induce improved biological responses. Both polarized hydroxyapatite (HA), whose surface charge is not dependent on loading, and piezoelectric ceramics, which produce electrical potentials under stress, have been studied in order to determine the possible benefits of using electrically active bioceramics as implant materials. The polarization of HA has a positive influence on interfacial responses to the ceramic. In vivo studies of polarized HA have shown polarized samples to induce improvements in bone ingrowth. The majority of piezoelectric ceramics proposed for implant use contain barium titanate (BaTiO(3)). In vivo and in vitro investigations have indicated that such ceramics are biocompatible and, under appropriate mechanical loading, induce improved bone formation around implants. The mechanism by which electrical activity influences biological responses is yet to be clearly defined, but is likely to result from preferential adsorption of proteins and ions onto the polarized surface. Further investigation is warranted into the use of electrically active ceramics as the indications are that they have benefits over existing implant materials.

Polarization of hydroxyapatite: influence on osteoblast cell proliferation.

Hydroxyapatite (HA) has been used clinically to treat bone defects. However, modifications of the surface properties of HA could improve and control bone matrix deposition and localized host tissue integration. The aim of this study was to investigate the effect of developing a surface charge on HA discs with respect to osteoblast activity in vitro. HA discs (12 mm x 2 mm) were sintered in either air or water vapour. The HA discs were then electrically polarized (positive and negative surfaces) or non-polarized (controls) and seeded with MC3T3-E1 cells. Polarized HA sintered in water vapour was shown to retain six times more charge than polarized HA sintered in air. Picogreen analysis demonstrated that at 4h cell number was significantly higher on the negatively and positively charged HA surface (water sintered) in comparison to the non-charged water and air-sintered HA controls. At 7 days there was a significant increase in cell number on the negatively charged HA (air sintered) sample in comparison to the negatively charged water vapour sintered HA sample and the non-charged water vapour sintered control sample. Also at 7 days, the picogreen data showed a significant increase in cell number on the positively charged water-treated HA sample in comparison to both the air- and water-treated HA non-charged control HA samples. An alamarBlue assay at 7 days demonstrated significant cell metabolic activity on the charged surfaces (both positive and negative) in comparison to the non-charged HA and the tissue culture plastic controls. This study demonstrated that all of the HA discs tested supported cell viability/attachment. However, cell attachment/proliferation/metabolic activity was significantly increased as a result of developing a charge on the HA surface.

Fabrication of HA/TCP scaffolds with a graded and porous structure using a camphene-based freeze-casting method.

A room temperature camphene-based freeze-casting method was used to fabricate hydroxyapatite/tricalcium phosphate (HA/TCP) ceramic scaffolds. By varying the solid loading of the mixture and the freezing temperature, a range of structures with different pore sizes and strength characteristics were achieved. The macropore size of the HA/TCP bioceramics was in the range of 100-200 microm, 40-80 microm and less than 40 microm at solid loadings of 10, 20 and 30 vol.%, respectively. The initial level of solid loading played a primary role in the resulting porosity of the scaffolds. The porosity decreased from 72.5 to 31.4 vol.% when the solid loading was increased from 10 to 30 vol.%. This resulted in an increase in the compressive strength from 2.3 to 36.4 MPa. The temperature gradient, rather than the percentage porosity, influenced the pore size distribution. The compressive strength increased from 1.95 to 2.98 MPa when samples were prepared at 4 degrees C as opposed to 30 degrees C. The results indicated that it was possible to manufacture porous HA/TCP bioceramics, with compressive strengths comparable to cancellous bone, using the freeze-casting manufacturing technique, which could be of significant clinical interest.

Electrical characterization of hydroxyapatite-based bioceramics.

This paper studies the AC conductivity and permittivity of hydroxyapatite (HA)-based ceramics from 0.1 Hz-1 MHz at temperatures from room temperature to 1000 degrees C. HA-based ceramics were prepared either as dense ceramics or in porous form with interconnected porosity and were sintered in either air or water vapour. Samples were thermally cycled to examine the influence of water desorption on AC conductivity and permittivity. Surface-bound water was thought to contribute to conductivity for both dense and porous materials at temperatures below 200 degrees C. At temperatures below 700 degrees C the permittivity and AC conductivity of HA was also influenced by the degree of dehydration and thermal history. At higher temperatures (700-1000 degrees C), bulk ionic conduction was dominant and activation energies were of the order of approximately 2 eV, indicating that hydroxyl ions are responsible for conductivity.

Flexible piezoelectric transducer for ultrasonic inspection of non-planar components.

This paper presents the fabrication and characterisation of a flexible ultrasonic transducer using commercially available PZT-5A piezoelectric fibers which are lapped to form rectangular piezoelectric elements. The key feature in the device construction is the inclusion of gaps between the piezoelectric fibers to ensure good flexibility in the plane normal to the fiber direction. The spatial response of the transducer ultrasonic output was assessed using acoustographic imaging. The flexibility of the transducer and its applicability in pulse-echo mode on curved sections was demonstrated by testing on a 38 mm diameter steel rod. The transducer response was found to be broad band and highly non uniform but good pulse-echo performance was achieved at 5 MHz.

Finite element modelling of dense and porous piezoceramic disc hydrophones.

The acoustic characteristics of dense and porous piezoceramic disc hydrophones have been studied by finite element modelling (FEM). The FEM results are validated initially by an analytical model for a simple disc of dense piezoceramic material and then it is extended to a porous piezoceramic disc replicating a foam-reticulated sample. Axisymmetric model was used for dense piezoceramic hydrophone due its regular geometric shape. 3-dimensional model was used for the porous piezoceramics, since the unit cell model is inadequate to fully represent transducers of finite lateral dimensions. The porous PZT discs have been synthesised by foam-reticulation technique. The electrical impedance and the receiving sensitivity of the hydrophones in water are evaluated in the frequency range 10-100 kHz. The model results are compared with the experimental data. The receiving sensitivity of piezocomposite hydrophones is found to be reasonably constant over the frequency range studied. The sharp resonance peaks observed for the dense piezoceramic hydrophone has broadened to a large extent for porous piezoceramic hydrophones, indicating higher losses. The flat frequency response suggests that the 3-3 piezocomposites are useful for wide-band hydrophone applications.

Anomalous power law dispersions in ac conductivity and permittivity shown to be characteristics of microstructural electrical networks.

The frequency dependent ac conductivity and permittivity of porous lead zirconate titanate ceramic with the pore volume filled with water are shown to match the simulated electrical response of a large network of randomly positioned resistors and capacitors. Anomalous power law dispersions in conductivity and permittivity are shown to be an electrical response characteristic of the microstructural network formed by the porous lead zirconate titanate pore structure. The anomalous power law dispersions of a wide range of materials are also suggested to be microstructural network characteristics.