MBE growth and characterization of InGaN-based films and nanocolumns on Silicon substrates and GaN templates

InN layers: MBE growth issues Growth of InN-based thin films: InN/InGaN QWS on GaN Growth of InN-based nanorods ● Self Self-assembled assembled InN InN nanorods nanorods onon different different substrates substrates ● Self-assembled InGaN nanorods ● Broad- Broad-emission emission nanostructures ● Self Self--assembled assembled InGaN InGaN--based based Qdisks Qdisks ● Selective area growth (SAG) of InGaN Qdisks

Electrocatalytic oxidation enhancement at the surface of InGaN films and nanostructures grown directly on Si(111)

Pronounced electrocatalytic oxidation enhancement at the surface of InGaN layers and nanostructures directly grown on Si by plasma-assisted molecular beam epitaxy is demonstrated. The oxidation enhancement, probed with the ferro/ferricyanide redox couple increases with In content and proximity of nanostructure surfaces and sidewalls to the c-plane. This is attributed to the corresponding increase of the density of intrinsic positively charged surface donors promoting electron transfer. Strongest enhancement is for c-plane InGaN layers functionalized with InN quantum dots (QDs). These results explain the excellent performance of our InN/InGaN QD biosensors and water splitting electrodes for further boosting efficiency.

Convective transport and stability in films of binary mixtures

Thin polymer films are increasingly used in advanced technological applications. The use of these films as coatings is often limited by their lack of stability due to their wettability properties on the substrates

Size and dimensionality effects in superconducting Mo thin films

Molybdenum is a low Tc, type I superconductor whose fundamental properties are poorly known. Its importance as an essential constituent of new high performance radiation detectors, the so-called transition edge sensors (TESs) calls for better characterization of this superconductor, especially in thin film form. Here we report on a study of the basic superconducting features of Mo thin films as a function of their thickness. The resistivity is found to rise and the critical temperature decreases on decreasing film thickness, as expected. More relevant, the critical fields along and perpendicular to the film plane are markedly different, thickness dependent and much larger than the thermodynamic critical field of Mo bulk. These results are consistent with a picture of type II 2D superconducting films, and allow estimates of the fundamental superconducting lengths of Mo. The role of morphology in determining the 2D and type II character of the otherwise type I molybdenum is discussed. The possible consequences of this behaviour on the performance of radiation detectors are also addressed

Aluminum slurry coatings to replace cadmium for aeronautic applications

Cadmium has been widely used as a coating to provide protection against galvanic corrosion for steels and for its natural lubricity on threaded applications. However, it is a toxic metal and a known carcinogenic agent, which is plated from an aqueous bath containing cyanide salts. For these reasons, the use of cadmium has been banned in Europe for most industrial applications. However, the aerospace industry is still exempt due to the stringent technical and safety requirements associated with aeronautical applications, as an acceptable replacement is yet to be found. Al slurry coatings have been developed as an alternative to replace cadmium coatings. The coatings were deposited on AISI 4340 steel and have been characterized by optical and electron microscopy. Testing included salt fog corrosion exposure, fluid corrosion exposure (immersion), humidity resistance, coating-substrate and paint-coating adhesion, electric conductivity, galvanic corrosion, embrittlement and fatigue. The results indicated that Al slurry coatings are an excellent alternative for Cd replacement.

Laser shock peening without absorbent coating (LSPwC) effect on 3D surface topography and mechanical properties of 6082-T651 Al alloy

The influence of nanosecond laser pulses applied by laser shock peening without absorbent coating (LSPwC) with a Q-switched Nd:YAG laser operating at a wavelength of λ = 1064 nm on 6082-T651 Al alloy has been investigated. The first portion of the present study assesses laser shock peening effect at two pulse densities on three-dimensional (3D) surface topography characteristics. In the second part of the study, the peening effect on surface texture orientation and micro-structure modification, i.e. the effect of surface craters due to plasma and shock waves, were investigated in both longitudinal (L) and transverse (T) directions of the laser-beam movement. In the final portion of the study, the changes of mechanical properties were evaluated with a residual stress profile and Vickers micro-hardness through depth variation in the near surface layer, whereas factorial design with a response surface methodology (RSM) was applied. The surface topographic and micro-structural effect of laser shock peening were characterised with optical microscopy, InfiniteFocus® microscopy and scanning electron microscopy (SEM). Residual stress evaluation based on a hole-drilling integral method confirmed higher compression at the near surface layer (33 μm) in the transverse direction (σmin) of laser-beam movement, i.e. − 407 ± 81 MPa and − 346 ± 124 MPa, after 900 and 2500 pulses/cm2, respectively. Moreover, RSM analysis of micro-hardness through depth distribution confirmed an increase at both pulse densities, whereas LSPwC-generated shock waves showed the impact effect of up to 800 μm below the surface. Furthermore, ANOVA results confirmed the insignificant influence of LSPwC treatment direction on micro-hardness distribution indicating essentially homogeneous conditions, in both L and T directions.

Laser Shock Processing influence on local properties and overall tensile behavior of friction stir welded joints

Based on laser beam intensities above 109 W/cm2 with pulse energy of several Joules and duration of nanoseconds, Laser Shock Processing (LSP) is capable of inducing a surface compressive residual stress field. The paper presents experimental results showing the ability of LSP to improve the mechanical strength and cracking resistance of AA2024-T351 friction stir welded (FSW) joints. After introducing the FSW and LSP procedures, the results of microstructural analysis and micro-hardness are discussed. Video Image Correlation was used to measure the displacement and strain fields produced during tensile testing of flat specimens; the local and overall tensile behavior of native FSW joints vs. LSP treated were analyzed. Further, results of slow strain rate tensile testing of the FSW joints, native and LSP treated, performed in 3.5% NaCl solution are presented. The ability of LSP to improve the structural behavior of the FSW joints is underscored.

Inorganic Photovoltaics - Planar and Nanostructured Devices

Since its invention in the 1950s, semiconductor solar cell technology has evolved in great leaps and bounds. Solar power is now being considered as a serious leading contender for replacing fossil fuel based power generation. This article reviews the evolution and current state, and potential areas of near future research focus, of leading inorganic materials based solar cells, including bulk crystalline, amorphous thin-films, and nanomaterials based solar cells. Bulk crystalline silicon solar cells continue to dominate the solar power market, and continued efforts at device fabrication improvements, and device topology advancements are discussed. III-V compound semiconductor materials on c-Si for solar power generation are also reviewed. Developments in thin-film based solar cells are reviewed, with a focus on amorphous silicon, copper zinc tin sulfide, cadmium telluride, as well as nanostructured Cadmium telluride. Recent developments in the use of nano-materials for solar power generation, including silicon and gallium arsenide nanowires, are also reviewed.

Ecotoxicology of pesticides on natural enemies of olive groves. Potential of ecdysone agonists for controlling Bactrocera oleae (Rossi) (Diptera: Tephritidae)

Pesticide applications are still one of the most common control methods against the main olive grove pests and diseases: the olive fruit fly, Bactrocera oleae (Rossi), the olive moth, Prays oleae (Bernard), the black scale, Saissetia oleae (Olivier), and the olive leaf spot, caused by the fungus Spilocaea oleagina Fries. However, and because the new pesticide legislation is aimed at an integrated pest and disease management, it is still important to evaluate and to know the ecotoxicology of pesticides on the natural enemies of the different agrosystems. A part of this work has been focusses on evaluating the direct and indirect effects of kaolin particle films and two copper-based products (Bordeaux mixture and copper oxychloride) through different laboratory, extended laboratory and semi-field experiments. Two natural enemies have been chosen: Psyttalia concolor (Szèpligeti), a parasitoid of the olive fruit fly, and Chilocorus nigritus (F.), predator of Diaspididae. This predator has been used instead of C. bipustulatus (L.), which is the species found in olive orchards. Kaolin mainly acts as a repellent of insects and/or as an oviposition deterrent. It is used in olive groves to control the olive fruit fly and the olive moth. Copper is applied against fungal and bacterial diseases. In olive groves it is used against the olive leaf spot and other diseases. No statistical differences were found in any of the experiments performed, compared to the controls, except when the oral toxicity of the products was evaluated on P. concolor females. In this case, kaolin and copper oxychloride caused a higher mortality 72 hours after the treatments, and both kaolin and the two copper formulations decreased females’ life span. Reproductive parameters were only negatively affected when kaolin was ingested. Apart from these experiments, due to the uncommon mode of action of kaolin, two extra experiments were carried out: a dual choice and a no-choice experiment. In this case, both P. concolor females and C. nigritus adults showed a clear preference for the untreated surfaces when they had the possibility of choosing between a treated surface and an untreated one. When there was no choice, no statistical differences were found between the treatments and the controls. Furthermore, the efficacy and the selectivity of three insect growth regulators (methoxyfenozide, tebufenozide and RH-5849) on B. oleae and P. concolor, respectively, have also been evaluated. In addition to laboratory experiments to evaluate the toxicity of the insecticides, also molecular approaches were used. RNA of both insects was isolated. cDNA was subsequently synthesized and the complete sequences of the ligand biding domain (LBD) of the ecdysone receptor of each insect were then determined. Afterwards the three dimensional structures of both LBDs were constructed. Finally, the docking of the insecticide molecules in the cavity delineated by the 12 α-helix that composed the LBD was performed. Both toxicity assays and molecular docking approaches showed that either methoxyfenozide or tebufenozide had no negative effects nor on B. oleae nor on P. concolor. In contrast, RH-5849 had no deleterious effect to the parasitoid but decreased olive fruit fly adults’ life span, especially when they were in contact with the fresh residue of the insecticide applied on a glass surface. The docking study of RH-5849 molecule has shown a very light hindrance with the wall of the LBD pocket. This means that this molecule could more or less adjust in the cavity. Thus, searching of new insecticides for controlling the olive fruit fly could be based on the basic lead structure of RH-5849 molecule.

Monitoring spinach shelf-life with hyperspectral image through

Different procedures for monitoring the evolution of leafy vegetables, under plastic covers during cold storage, have been studied. Fifteen spinach leaves were put inside Petri dishes covered with three different plastic films and stored at 4 °C for 21 days. Hyperspectral images were taken during this storage. A radiometric correction is proposed in order to avoid the variation in transmittance of the plastic films during time in the hyperspectral images. Afterwards, three spectral pre-processing procedures (no pre-process, Savitsky–Golay and Standard Normal Variate, combined with Principal Component Analysis) were applied to obtain different models. The corresponding artificial images of scores were studied by means of Analysis of Variance to compare their ability to sense the aging of the leaves. All models were able to monitor the aging through storage. Radiometric correction seemed to work properly and could allow the supervision of shelf-life in leafy vegetables through commercial transparent films.

Compatibilidad de Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) y Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae), importantes enemigos naturales de la mosca blanca Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) en cultivos hortícolas, con nuevas barreras físicas selectivas y modernos plaguicidas

Los programas de Gestión Integrada de Plagas (GIP) promueven el uso de estrategias de control que sean respetuosas con el medio ambiente, sin embargo el uso de insecticidas en los cultivos hortícolas sigue siendo necesario para el control de determinadas plagas, como es el caso de la mosca blanca Bemisia tabaci (Gennadius). Por ello, el objetivo de esta tesis es el estudio de la integración de las tres estrategias de control más empleadas hoy en día para el control de plagas: el control biológico, el físico y el químico. Una primera parte de este trabajo ha consistido en el estudio de los efectos letales y subletales de once insecticidas, aplicados a la dosis máxima de campo, sobre los enemigos naturales Eretmocerus mundus Mercet y Amblyseius swirskii Athias-Henriot, mediante ensayos de laboratorio y persistencia (laboratorio extendido). Para la evaluación de la toxicidad de los insecticidas sobre los estados de vida más protegidos de estos enemigos naturales, se trataron bajo la Torre de Potter las pupas de E. mundus y los huevos de A. swirskii. Además, se llevaron a cabo ensayos de contacto residual para determinar los efectos letales y subletales de estos insecticidas sobre el estado adulto de ambas especies de enemigos naturales. Para ello, los pesticidas se aplicaron sobre placas de cristal (laboratorio) o sobre plantas (laboratorio extendido: persistencia). Los resultados mostraron que los insecticidas flonicamida, flubendiamida, metaflumizona, metoxifenocida, spiromesifen y spirotetramat eran compatibles con el estado de pupa de E. mundus (OILB 1: Inocuos). Sin embargo, abamectina, deltametrina y emamectina fueron categorizadas como ligeramente tóxicas (OILB 2) al causar efectos deletéreos. Los dos pesticidas más tóxicos fueron spinosad y sulfoxaflor, los cuales redujeron significativamente la emergencia de las pupas tratadas (OILB 4: Tóxicos). Flonicamida, flubendiamida, metoxifenocida y spiromesifen fueron compatibles con el estado adulto de E. mundus (OILB 1: Inocuos). Abamectina, deltametrina, emamectina, metaflumizona y spiromesifen pueden ser recomendados para su uso en programas de GIP, si se usan los plazos de seguridad apropiados, de acuerdo con la persistencia de cada uno de estos insecticidas, antes de la liberación del enemigo natural. Al contrario, spinosad y sulfoxaflor no resultaron ser compatibles (OILB D: Persistentes), aunque la realización de ensayos adicionales es necesaria para ver los efectos de los mismos en campo. Todos los insecticidas estudiados, excepto el spirotetramat (OILB 2: Ligeramente tóxico), fueron selectivos para el estado de huevo de A. swirskii (OILB 1: Inocuos). Flonicamida, flubendiamida, metaflumizona, metoxifenocida, spiromesifen, spirotetramat y sulfoxaflor, fueron compatibles con el estado adulto de A. swirskii (OILB 1: Inocuos). Abamectina, deltametrina, emamectina y spinosad pueden ser recomendados para su uso en programas de GIP, si se usan los plazos de seguridad apropiados, de acuerdo con la persistencia de cada uno de estos insecticidas, antes de la liberación del enemigo natural. Entre las nuevas estrategias de la GIP, los plásticos y mallas fotoselectivas han demostrado ser una herramienta importante para el control de plagas y enfermedades en cultivos hortícolas protegidos. Por ello, en una segunda parte de este trabajo, se estudiaron tanto los efectos directos, como la combinación de efectos directos y mediados por planta y plaga de ambientes pobres en luz UV, en presencia o ausencia del Virus del rizado amarillo del tomate (TYLCV), sobre E. mundus. En primer lugar, se realizó un ensayo al aire libre para la evaluación de la capacidad de vuelo de E. mundus en cajas tipo túnel (1 x 0,6 x 0,6 m) cubiertas con distintas barreras absorbentes de luz UV. Se detectó un efecto directo en la capacidad de orientación de E. mundus, debido a que este parasitoide utiliza estímulos visuales para localizar a sus huéspedes, únicamente en las barreras que bloqueaban más del 65% de la luz UV (malla G). En segundo lugar, bajo condiciones de invernadero, se evaluó la combinación de efectos directos y mediados por planta y plaga sobre E. mundus, usando plantas de tomate sanas o infectadas con el TYLCV y cajas (30 x 30 x 60 cm) cubiertas con los distintos plásticos fotoselectivos. En este caso, no se observó ningún efecto en la capacidad benéfica del parasitoide cuando este estaba en contacto con plantas de tomate infestadas con ninfas de B. tabaci, lo que demuestra que este insecto usa estímulos táctiles para encontrar a sus huéspedes a cortas distancias. Además, las diferentes condiciones de radiación UV estudiadas tuvieron cierto impacto en la morfología, fisiología y bioquímica de las plantas de tomate, infestadas o no con el virus de la cuchara, detectándose pequeñas alteraciones en alguno de los parámetros estudiados, como el peso fresco y seco, el contenido en H y el espesor de las cutículas y de las paredes celulares de la epidermis foliar. Por último, no se observaron efectos de la radiación UV mediados por planta, ni en B. tabaci ni en su parasitoide, E. mundus. En una tercera parte, se evaluaron los efectos de una malla tratada con bifentrin sobre ambos enemigos naturales, en ensayos de laboratorio, semicampo y campo. Las mallas tratadas fueron diseñadas originariamente para el control de mosquitos vectores de la malaria, y actualmente se está trabajando para su uso en agricultura, como una nueva estrategia de control de plagas. En ensayos de laboratorio, cuando adultos de E. mundus y A. swirskii se expusieron por contacto durante 72 horas con la malla tratada (cajas de 6 cm diámetro), se registró una alta mortalidad. Sin embargo, en el ensayo de preferencia, estos enemigos naturales no fueron capaces de detectar la presencia de bifentrin y, en aquellos individuos forzados a atravesar la malla tratada, no se observó mortalidad a corto plazo (72 horas). En estudios de semicampo, llevados a cabo bajo condiciones de invernadero en cajas de 25 x 25 x 60 cm de altura, la capacidad benéfica de E. mundus no se vio afectada. Finalmente, en ensayos de campo llevados a cabo en invernaderos comerciales (4000m2) en Almería, A. swirskii no se vio afectado por la presencia en el cultivo de la malla tratada con bifentrin y los niveles de infestación de B. tabaci y F. occidentalis detectados bajo dicha malla, fueron inferiores a los del control. Por último, se ha evaluado la composición de la microflora bacteriana de tres especies de parasitoides, E. mundus, Eretmocerus eremicus Rose & Zolnerowich y Encarsia formosa Gahan, y la influencia de la misma en su susceptibilidad a insecticidas. Se llevó a cabo una extracción total de ADN de los insectos y la región variable V4 del ARNr se amplificó usando cebadores universales bacterianos. Para identificar las secuencias de los géneros bacterianos presentes en los parasitoides, se realizó una Next Generation sequencing (Illumina sequencing). Una vez identificados los géneros bacterianos, el gen ADNr 16S de las Actinobacterias se amplificó del ADN extraído de los insectos, usando cebadores universales bacterianos y específicos de Actinobacterias, y los productos de la Nested PCR fueron clonados para identificar todas las especies del género Arthrobacter. Tres bacterias (A. aurescens Phillips, A. nicotinovarans Kodama, Yamamoto, Amano and Amichi y A. uratoxydans Stackebrandt, Fowler, Fiedler and Seiler), próximas a las especies de Arthrobacter presentes en los parasitoides, se obtuvieron de la colección bacteriana del BCCMTM/LMG y se midió su actividad esterasa. Finalmente, se realizaron ensayos con antibióticos (tetraciclina) y de contacto residual con insecticidas (abamectina) para determinar la influencia de las especies de Arthrobacter en la susceptibilidad de E. mundus a insecticidas. Los resultados muestran que este género bacteriano puede afectar a la toxicidad de E. mundus a abamectina, mostrando la importancia de la comunidad microbiana en enemigos naturales, factor que debe ser considerado en los estudios de evaluación de los riesgos de los insecticidas. ABSTRACT Integrated Pest Management (IPM) programs promote the use of control strategies more respectful with the environment; however the use of insecticides in vegetable crops is still needed to control certain pests, such as the whitefly Bemisia tabaci (Gennadius). Therefore, the objective of this work is to study the integration of the three most commonly used pest control strategies nowadays: biological, physical and chemical control. Firstly, the lethal and sublethal effects of eleven insecticides, applied at their maximum field recommended concentration, on the parasitic wasp Eretmocerus mundus Mercet and the predator Amblyseius swirskii Athias-Henriot has been assessed in the laboratory and in persistence tests (extended laboratory). To test the effects of pesticides on the most protected life stage of these natural enemies, E. mundus pupae and A. swirskii eggs were sprayed under a Potter precision spray tower. Laboratory contact tests were therefore conducted to determine the lethal and sublethal effects of these pesticides on the adult stage of these natural enemies. In the residual contact tests the pesticides were applied on glass plates (laboratory) or plants (extended laboratory: persistence). The study showed that the insecticides flonicamid, flubendiamide, metaflumizone, methoxyfenozide, spiromesifen and spirotetramat were selective for E. mundus pupae (IOBC 1: Harmless). Nevertheless, abamectin, deltamethrin and emamectin were categorized as slightly harmful (IOBC 2) due to the deleterious effects caused. The two most harmful pesticides were spinosad and sulfoxaflor, which significantly reduced the adult emergence from treated pupae (IOBC 4: Harmful). Flonicamid, flubendiamide, methoxyfenozide and spiromesifen were compatible with E. mundus adults (IOBC 1: Harmless). Base on the duration of the harmful activity, abamectin, deltamethrin, emamectin, metaflumizone and spirotetramat could be recommended for use in IPM programs if appropriate safety deadlines are used before the natural enemy release. On the contrary, spinosad and sulfoxaflor were not compatible (IOBC D: persistent), although additional studies are required to determine their effects under field conditions. All the pesticides tested, except spirotetramat (IOBC 2: Slightly harmful), were selective for A. swirskii eggs (IOBC 1: Harmless). Flonicamid, flubendiamide, metaflumizone, methoxyfenozide, spiromesifen, spirotetramat and sulfoxaflor were compatible with A. swirskii adults (IOBC 1: Harmless). However, abamectin, deltamethrin, emamectin and spinosad could be recommended for use in IPM programs if appropriate safety deadlines are used before the natural enemy release. Among new IPM strategies, UV-absorbing photoselective plastic films and nets have been shown to be an important tool for the control of pests and diseases in horticultural protected crops. Because of that, we secondly studied the plant and pest insect-mediated and/or the direct effects on E. mundus under different UV radiation conditions, in presence or absence of the Tomato Yellow Leaf Curl Virus (TYLCV). In the first experiment, performed outdoors, the flight activity of E. mundus was studied in one-chamber tunnels (1 x 0.6 x 0.6 m) covered with different photoselective barriers. Because E. mundus uses visual cues for host location at a long distance, a direct effect on its host location ability was detected, but only in the UV-absorbing barriers blocking more than 65% of the UV light (G net). In a second experiment, the direct and plant and pest insect-mediated effects of different UV radiation conditions on E. mundus were studied, inside cages (30 x 30 x 60 cm) covered with the different UVplastic films and under greenhouse conditions, using healthy or TYLCV-virus infected tomato plants. In this case, not any effect on the beneficial capacity of this parasitoid was detected, proving that he uses tactile cues at a short distance of the host. Moreover, the different UV radiation conditions studied had a certain direct impact in the morphology, physiology and biochemistry of tomato plants infested or not with the TYLCV, and small alterations in some parameters such as fresh and dry weight, H percentage and cuticle and cell wall thickness of epidermal cells of the leaves, were detected. Finally, none plant-mediated UV effects neither in the whitefly B. tabaci nor in their parasitic wasp were found. Thirdly, the effects of a bifenthrin treated net were evaluated in different laboratory, semi-field and field experiments on the natural enemies studied. Treated nets were developed long time ago aiming at the control of the mosquitoes vectors of malaria, and nowadays, there is a great interest on assessing the possibility of their use in agriculture. In laboratory assays, a high mortality was recorded when E. mundus and A. swirskii adults were exposed by contact to the bifenthrin treated net for 72 hours in small cages (12 cm diameter). However, these natural enemies were not able to detect the presence of bifenthrin in a dual-choice test and no short-term mortality (72 hours) was recorded in those individuals that went through the treated net. In semi-field assays, performed under greenhouse conditions with cages of 25 x 25 x 60 cm high, the beneficial capacity of E. mundus was not affected. Finally, in field assays carried out in commercial multispan greenhouses (4000 m2) in Almería, A. swirskii was not affected by the presence of the bifenthrin treated net in the crop and the B. tabaci and F. occidentalis infestation levels were significantly lower than in the control. Finally, the composition of the microflora present in three species of parasitoids, E. mundus, Eretmocerus eremicus Rose & Zolnerowich and Encarsia formosa Gahan, and its influence in their susceptibility to insecticides, have been assessed. A total DNA extraction was performed on insects and universal bacterial primers were used to amplify the variable V4 region of the rRNA. A Next Generation sequencing (Illumina sequencing) was performed to identify the sequences of the bacterial genera present in the parasitic wasps. Once, the bacterial genera were identified, 16S rDNA gene of Actinobacteria were amplified from insects DNA extracts using the universal bacterial and actinobacterial primers, and the nested PCR products, were cloned to identify the Arthrobacter species. Three bacteria (A. aurescens Phillips, A. nicotinovarans Kodama, Yamamoto, Amano and Amichi and A. uratoxydans Stackebrandt, Fowler, Fiedler and Seiler), having the closest match with the Arthrobacter species present in the parasitic wasps, were obtained from the BCCMTM/LMG bacteria collection and its esterase activity was measured. Finally, antibiotic and residual contact tests were done to determine the influence of Arthrobacter species in the susceptibility of E. mundus to pesticides (abamectin). The results suggest that this bacterial genus can affect the toxicity of E. mundus to abamectin, which in turn supports the importance of the microbial community in natural enemies that it should be considered as a factor in risk assessment tests of pesticides.