Effect of different modification by gold nanoparticles on the electrochemical performance of screen-printed sensors with boron-doped diamond electrode.

Screen-printed sensors with chemically deposited boron-doped diamond electrodes (BDDE) were modified with different types of gold nanoparticles (AuNPs) according to a new original procedure. Physically and electrochemically deposited AuNPs had various sizes and also nanoporous character. They also differ in shape and density of surface coverage. The developed sensors were characterized using scanning electron microscopy and Raman spectroscopy. Their electrochemical properties were studied using cyclic voltammetry and electrochemical impedance spectrometry of selected outer sphere ([Ru(NH3)6]Cl3) and inner sphere (K3[Fe(CN)6], dopamine) redox markers. The application possibilities of such novel screen-printed sensors with BDDE modified by AuNPs were verified in the analysis of the neurotransmitter dopamine. The best analytical performance was achieved using printed sensors modified with the smallest AuNPs. The achieved limit of detection values in nanomolar concentrations (2.5 nmol L-1) are much lower than those of unmodified electrodes, which confirms the significant catalytic effects of gold nanoparticles on the surface of the working electrode. Sensors with the best electrochemical properties were successfully applied in the analysis of a model solution and spiked urine samples.

Charge Trap States of SiC Power TrenchMOS Transistor under Repetitive Unclamped Inductive Switching Stress.

Silicon carbide (SiC) has been envisioned as an almost ideal material for power electronic devices; however, device reliability is still a great challenge. Here we investigate the reliability of commercial 1.2-kV 4H-SiC MOSFETs under repetitive unclamped inductive switching (UIS). The stress invoked degradation of the device characteristics, including the output and transfer characteristics, drain leakage current, and capacitance characteristics. Besides the shift of steady-state electrical characteristics, a significant change in switching times points out the charge trapping phenomenon. Transient capacitance spectroscopy was applied to investigate charge traps in the virgin device as well as after UIS stress. The intrinsic traps due to metal impurities or Z1,2 transitions were recognized in the virgin device. The UIS stress caused suppression of the second stage of the Z1,2 transition, and only the first stage, Z10, was observed. Hence, the UIS stress is causing the reduction of multiple charging of carbon vacancies in SiC-based devices.

Evaluation of Effective Mass in InGaAsN/GaAs Quantum Wells Using Transient Spectroscopy.

Transient spectroscopies are sensitive to charge carriers released from trapping centres in semiconducting devices. Even though these spectroscopies are mostly applied to reveal defects causing states that are localised in the energy gap, these methods also sense-charge from quantum wells in heterostructures. However, proper evaluation of material response to external stimuli requires knowledge of material properties such as electron effective mass in complex structures. Here we propose a method for precise evaluation of effective mass in quantum well heterostructures. The infinite well model is successfully applied to the InGaAsN/GaAs quantum well structure and used to evaluate electron effective mass in the conduction and valence bands. The effective mass m/m0 of charges from the conduction band was 0.093 ± 0.006, while the charges from the valence band exhibited an effective mass of 0.122 ± 0.018.

Photoresponse Dimensionality of Organic Field-Effect Transistor.

Organic field-effect transistors have been envisioned for advanced photodetectors because the organic semiconductors provide unique absorption characteristics, low-cost fabrication, or compatibility with flexible substrates. However, the response time of organic phototransistors still does not reach the required application level. Here, we report the photoresponse of copper phthalocyanine phototransistor in a steady state and under pulsed illumination. The detailed analysis based on the random walk among a field of traps was used to evaluate the dimensionality of electron transport in a device.

Synthesis and Effect of the Structure of Bithienyl-Terminated Surfactants for Dielectric Layer Modification in Organic Transistor.

A series of bithienyl-terminated surfactants with various alkyl chain lengths (from C8 to C13) and phosphono or chlorodimethylsilyl anchoring groups were synthesized by palladium-catalyzed hydrophosphonation, or platinum-catalyzed hydrosilylation as a key step. Surfactants were tested in pentacene or α-sexithiophene-based organic field-effect transistors (OFETs) for the modification of the dielectric surface. The studied surfactants increased the effective mobility of the α-sexithiophene-based device by up to one order of magnitude. The length of alkyl chain showed to be significant for the pentacene-based device, as the effective mobility only increased in the case of dielectric modification with bithienylundecylphosphonic acid. AFM allowed a better understanding of the morphology of semiconductors on bare SiO2 and surfaces treated with bithienylundecylphosphonic acid.

4-Azafluorenone and α-Carboline Fluorophores with Green and Violet/Blue Emission.

The emission properties of three 4-azafluorenone and five new α-carboline fluorophores in both solution and thin solid films were investigated. Fluorescence of the azafluorenone is clearly enhanced in thin solid films due to the presence of phenyl/biphenyl rotors, and these derivatives can be classified as green Aggregation-Induced Emission luminogens (AIEgens) with a non-emissive heteroaromatic core structure. Compared to azafluorenones, emission of α-carbolines is hypsochromically shifted to the blue region of the electromagnetic spectrum, and most of these derivatives exhibit strong violet-blue fluorescence in both solution and thin solid film layers. Further, the effective mobility and electroluminescence of new α-carbolines were investigated in prepared organic field-effect transistors and organic light-emitting diodes, respectively.

Treating great and small saphenous vein insufficiency with histoacryl in patients with symptomatic varicose veins and increased risk of surgery.

BACKGROUND: Treating great and small saphenous vein trunk insufficiency with cyanoacrylate glue is the least taxing treatment method of all available techniques. Due to long-term unavailability of commercial kits with n-butyl-2-cyanoacrylate (histoacryl) in the Czech Republic, we used a modified technique. PATIENTS AND METHODS: Fifty-six limbs in 49 patients suffering from great saphenous vein or small saphenous vein insufficiency in combination with symptomatic chronic venous insufficiency and complicating comorbidities were treated with a modified endovascular cyanoacrylate glue application technique. RESULTS: The immediate success rate of the treatment was 98 %. In follow-up intervals of six weeks, six months, one year, and two years, the anatomical success rates of embolization (recanalization of no more than 5 cm of the junction) were 98, 96, 94, and 94 %, respectively. At identical intervals the venous insufficiency was scored according to the Aberdeen Varicose Vein Questionnaire and the American Venous Clinical Severity Score. In both cases, improvement was demonstrated over the two-year follow-up, with a 0.5 % significance level. Specific clinical signs of venous insufficiency were also evaluated, such as pain, oedema, clearance of varicose veins, and healing of venous ulceration. One severe complication - a pulmonary embolism - was reported, without consequences. CONCLUSIONS: We demonstrated that treating insufficient saphenous veins with modified histoacryl application brought a relief from symptoms of venous insufficiency and that the efficiency of this technique is comparable to commonly used methods.

Charge injection and transport properties of an organic light-emitting diode.

The charge behavior of organic light emitting diode (OLED) is investigated by steady-state current-voltage technique and impedance spectroscopy at various temperatures to obtain activation energies of charge injection and transport processes. Good agreement of activation energies obtained by steady-state and frequency-domain was used to analyze their contributions to the charge injection and transport. We concluded that charge is injected into the OLED device mostly through the interfacial states at low voltage region, whereas the thermionic injection dominates in the high voltage region. This comparison of experimental techniques demonstrates their capabilities of identification of major bottleneck of charge injection and transport.

Estimating economic thresholds for site-specific weed control using manual weed counts and sensor technology: an example based on three winter wheat trials.

BACKGROUND: Precision experimental design uses the natural heterogeneity of agricultural fields and combines sensor technology with linear mixed models to estimate the effect of weeds, soil properties and herbicide on yield. These estimates can be used to derive economic thresholds. Three field trials are presented using the precision experimental design in winter wheat. Weed densities were determined by manual sampling and bi-spectral cameras, yield and soil properties were mapped. RESULTS: Galium aparine, other broad-leaved weeds and Alopecurus myosuroides reduced yield by 17.5, 1.2 and 12.4 kg ha(-1) plant(-1) m(2) in one trial. The determined thresholds for site-specific weed control with independently applied herbicides were 4, 48 and 12 plants m(-2), respectively. Spring drought reduced yield effects of weeds considerably in one trial, since water became yield limiting. A negative herbicide effect on the crop was negligible, except in one trial, in which the herbicide mixture tended to reduce yield by 0.6 t ha(-1). Bi-spectral cameras for weed counting were of limited use and still need improvement. Nevertheless, large weed patches were correctly identified. CONCLUSION: The current paper presents a new approach to conducting field trials and deriving decision rules for weed control in farmers' fields.

Potential use of ground-based sensor technologies for weed detection.

Site-specific weed management is the part of precision agriculture (PA) that tries to effectively control weed infestations with the least economical and environmental burdens. This can be achieved with the aid of ground-based or near-range sensors in combination with decision rules and precise application technologies. Near-range sensor technologies, developed for mounting on a vehicle, have been emerging for PA applications during the last three decades. These technologies focus on identifying plants and measuring their physiological status with the aid of their spectral and morphological characteristics. Cameras, spectrometers, fluorometers and distance sensors are the most prominent sensors for PA applications. The objective of this article is to describe-ground based sensors that have the potential to be used for weed detection and measurement of weed infestation level. An overview of current sensor systems is presented, describing their concepts, results that have been achieved, already utilized commercial systems and problems that persist. A perspective for the development of these sensors is given.

Development and testing of a decision making based method to adjust automatically the harrowing intensity.

Harrowing is often used to reduce weed competition, generally using a constant intensity across a whole field. The efficacy of weed harrowing in wheat and barley can be optimized, if site-specific conditions of soil, weed infestation and crop growth stage are taken into account. This study aimed to develop and test an algorithm to automatically adjust the harrowing intensity by varying the tine angle and number of passes. The field variability of crop leaf cover, weed density and soil density was acquired with geo-referenced sensors to investigate the harrowing selectivity and crop recovery. Crop leaf cover and weed density were assessed using bispectral cameras through differential images analysis. The draught force of the soil opposite to the direction of travel was measured with electronic load cell sensor connected to a rigid tine mounted in front of the harrow. Optimal harrowing intensity levels were derived in previously implemented experiments, based on the weed control efficacy and yield gain. The assessments of crop leaf cover, weed density and soil density were combined via rules with the aforementioned optimal intensities, in a linguistic fuzzy inference system (LFIS). The system was evaluated in two field experiments that compared constant intensities with variable intensities inferred by the system. A higher weed density reduction could be achieved when the harrowing intensity was not kept constant along the cultivated plot. Varying the intensity tended to reduce the crop leaf cover, though slightly improving crop yield. A real-time intensity adjustment with this system is achievable, if the cameras are attached in the front and at the rear or sides of the harrow.

Nonequilibrium phases of nanoparticle Langmuir films.

We report on an in-situ observation of the colloidal silver nanoparticle self-assembly into a close-packed monolayer at the air/water interface followed by a 2D to 3D transition. Using the fast tracking GISAXS technique, we were able to observe the immediate response to the compression of the self-assembled nanoparticle layer at the air/water interface and to identify all relevant intermediate stages including those far from the equilibrium. In particular, a new nonequilibrium phase before the monolayer collapse via the 2D to 3D transition was found that is inaccessible by the competing direct space imaging techniques such as the scanning and transmission electron microscopies due to the high water vapor pressure and surface tension.

An ultrasonic system for weed detection in cereal crops.

Site-specific weed management requires sensing of the actual weed infestation levels in agricultural fields to adapt the management accordingly. However, sophisticated sensor systems are not yet in wider practical use, since they are not easily available for the farmers and their handling as well as the management practice requires additional efforts. A new sensor-based weed detection method is presented in this paper and its applicability to cereal crops is evaluated. An ultrasonic distance sensor for the determination of plant heights was used for weed detection. It was hypothesised that the weed infested zones have a higher amount of biomass than non-infested areas and that this can be determined by plant height measurements. Ultrasonic distance measurements were taken in a winter wheat field infested by grass weeds and broad-leaved weeds. A total of 80 and 40 circular-shaped samples of different weed densities and compositions were assessed at two different dates. The sensor was pointed directly to the ground for height determination. In the following, weeds were counted and then removed from the sample locations. Grass weeds and broad-leaved weeds were separately removed. Differences between weed infested and weed-free measurements were determined. Dry-matter of weeds and crop was assessed and evaluated together with the sensor measurements. RGB images were taken prior and after weed removal to determine the coverage percentages of weeds and crop per sampling point. Image processing steps included EGI (excess green index) computation and thresholding to separate plants and background. The relationship between ultrasonic readings and the corresponding coverage of the crop and weeds were assessed using multiple regression analysis. Results revealed a height difference between infested and non-infested sample locations. Density and biomass of weeds present in the sample influenced the ultrasonic readings. The possibilities of weed group discrimination were assessed by discriminant analysis. The ultrasonic readings permitted the separation between weed infested zones and non-infested areas with up to 92.8% of success. This system will potentially reduce the cost of weed detection and offers an opportunity to its use in non-selective methods for weed control.

Study of relaxation process of dipalmitoyl phosphatidylcholine monolayers at air-water interface: effect of electrostatic energy.

The instability of organic monolayer composed of polar molecules at the air-water interface has been a spotlight in interface science for many decades. However, the effect of electrostatic energy contribution to the free energy in the system is still not understood. Herein, we investigate the mechanical and electrical properties by studying the isobaric relaxation process of a dipalmitoyl phosphatidylcholine monolayer on water subphase with various concentrations of divalent ions to reveal the effect of electrostatic energy on thermodynamics and kinetics of the collapse mechanism. Our results demonstrate that electrical energy among the dipolar molecules plays an important role in the stability of monolayer and enhances the formation of micelles into subphase under high pressure. In addition, to confirm the electrostatic energy contribution, the well-known thermal effect on the stability of the film is compared. Hence, the general description of the monolayer free energy with contribution of electrostatic energy is suggested to describe the phase transition.

Multi-dimensional PARAFAC2 component analysis of multi-channel EEG data including temporal tracking.

The identification of signal components in electroencephalographic (EEG) data originating from neural activities is a long standing problem in neuroscience. This area has regained new attention due to the possibilities of multi-dimensional signal processing. In this work we analyze measured visual-evoked potentials on the basis of the time-varying spectrum for each channel. Recently, parallel factor (PARAFAC) analysis has been used to identify the signal components in the space-time-frequency domain. However, the PARAFAC decomposition is not able to cope with components appearing time-shifted over the different channels. Furthermore, it is not possible to track PARAFAC components over time. In this contribution we derive how to overcome these problems by using the PARAFAC2 model, which renders it an attractive approach for processing EEG data with highly dynamic (moving) sources.

Information system for monitoring environmental impacts of genetically modified organisms.

BACKGROUND, AIM AND SCOPE: European legislation stipulates that genetically modified organisms (GMO) have to be monitored to identify potential adverse environmental effects. A wealth of different types of monitoring data from various sources including existing environmental monitoring programmes is expected to accumulate. This requires an information system to efficiently structure, process and evaluate the monitoring data. METHODS: A structure for an Information System for Monitoring GMO (ISMO) was developed by a multidisciplinary research team. It is based on the requirement to organise all relevant information in a logical, readily accessible and functional manner. RESULTS: For the ISMO, we present a combination of three interrelated components: Firstly, an ISMO should comprise a knowledge database structured according to information related to the different scale levels of biological organisation relevant to GMO monitoring and scientific hypotheses on cause-effects which should be validated by monitoring data. Secondly, a monitoring database should be part of an ISMO containing GMO-specific monitoring data and meta-data. This monitoring database should be linked with monitoring data from other monitoring programmes which are relevant for GMO-related questions. Thirdly, an ISMO should encompass a database covering administrative and procedural data. Neither national nor international approaches to an ISMO exist yet. CONCLUSIONS: An ISMO as designed in this paper could support competent authorities in both the GMO notification process and in post-market monitoring. This includes evaluating the environmental risks of experimentally releasing GMO and placing them on the market, assessing monitoring plans and evaluating monitoring results. The ISMO should be implemented on both the national and international level, preferably combining different administrative scales. Harmonisation approaches towards GMO monitoring data are at an initial stage, but they are a precondition to coordinated GMO monitoring and to successfully implementing an ISMO. It is recommended to set up a legal basis and to agree on common strategies for the data coordination and harmonisation.

Effect of external electrostatic charge on condensed phase domains at the air-water interface: Experiment and shape equation analysis.

The effect of external electrostatic charge on the shapes of liquid condensed (LC) phase domains in monolayer at the air/water interface was investigated. For this reason the thermodynamic properties, domain size, and spontaneous polarization were analyzed by surface pressure-area isotherms, Brewster angle microscopy (BAM), and Maxwell displacement current technique. The analysis indicated magnesium ions preferred to bond with dipalmitoyl phosphatidylcholine negative head group in liquid expanded phase and/or at domain boundary at low ion concentration and got an access to binding with molecules inside of the LC domains for higher ion concentration. Domain size increase characterized by BAM was discussed in respect to the shape equation on the basis of electrostatic energy contribution. Although molecular repulsive force increased by adding of ions into subphase, the growth of domain size exceeded this tendency. Following shape equation analysis it was suggested that this effect corresponded to change in dipole moment orientation represented by increase in spontaneous polarization in normal projection. This demonstrated impact of local electrostatic field on molecular dipoles and free energy of LC domains.

Dipolar electrostatic energy effect on relaxation process of monolayers at air-water interface: analysis of thermodynamics and kinetics.

In order to understand the effect of electrostatic energy on phase transition from monolayer to multilayer, isobaric relaxation process of Langmuir monolayers composed of stearic acid or ferroelectric polyvinylidene fluoride and trifluoroethylene copolymer with various vinylidene fluoride (VDF) ratios is investigated in terms of thermodynamic and kinetic analysis. A monotonous decreasing tendency of material loss with respect to temperature is observed for stearic acid monolayer, which is due to thermal activation effect on phase transition from monolayer to multilayer. In contrast, for the ferroelectric monolayer it presents a nonmonotonous behavior of losing materials with a peak position near the Curie temperature, which is not only owing to thermal activation but also dipole moment change. This observation is confirmed for the copolymer monolayers with other VDF content ratios. Amazingly, for the ferroelectric monolayers a good correspondence is found for critical temperatures evaluated from several independent methods including the analysis on slow collapse. This finding again tells the fact that the relaxation process, namely phase transition from monolayer to multilayer, is greatly influenced by dipolar electrostatic energy. Moreover, the study of time dependent relaxation process reveals a diffusionlike behavior of multilayer structure formation, which cannot be interpreted by classical models. Hence a new model based on diffusion-driven material transfer is proposed and diffusivity of the copolymer molecules is estimated with a value of 0.4x10(-5) cm(2)/s. As a whole, this research reflects the importance of dipolar electrostatic energy for phase transition of monolayers at air-water interface.

Electrostatic Maxwell stress model of the shapes of condensed phase domains in monolayers at the air-water interface.

The formation mechanism of the shapes of condensed phase domains in monolayers at the air-water interface was investigated taking into account the surface pressure, line tension, and electrostatic energy due to the spontaneous polarization generated in normal and in-plane direction. By deriving the shape equation of monolayer domains as the mechanical balance at the domain boundary, we found that the electrostatic energy contributes to the shape equation as electrostatic Maxwell stress. Development of a cusp from condensed phase domains of fatty acid monolayers, which has been experimentally observed, was analyzed by the shape equation. It was found that the development of a cusp originated from the strong Maxwell stress, which was induced by the non-uniform orientational distribution in the fatty acid domain, and that cusped shapes gave a minimum of the free energy of the domain. It demonstrates that the shape equation with Maxwell stress, which is derived in the present study, is useful to study the formation mechanism of the shapes of condensed phase domains in monolayers.

Orientation ordering of nanoparticle Ag/Co cores controlled by electric and magnetic fields.

The effect of electric and magnetic fields on the sandwich structure Pt/hydrogenated amorphous silicon (a-Si:H)/stearic acid monolayer/Langmuir-Blodgett film of Ag/Co nanoparticles encapsulated in an organic envelope is studied. This structure is used as a working electrode in an electrochemical cell filled with NaCl solution (1 mM) and equipped with an Ag/AgCl reference electrode. Reversible changes in voltammograms are observed due to treatments (negative or positive bias voltage and simultaneous laser irradiation) applied to the designed structure before measurements. As an explanation of the observed phenomena we suggest that both the Co-up and Ag-up (on the a-Si:H surface) orientation orderings of nanoparticle Ag/Co cores are repeatedly reached. The role of the photovoltaic material (a-Si:H) in the observed behavior is explained. Voltammetric measurements with an applied magnetic field support our idea about the orientation ordering of nanoparticle cores.