Queen-worker conflict over sex ratio: a comparison of primary and secondary sex ratios in the Argentine ant,

We compare the primary sex ratio (proportion o haploid eggs laid by queens) and the secondary sex ratio (proportion of male pupae produced) in the Argentine ant Iridomyrmex humilis with the aim of investigating whether workers control the secondary sex ratio by selectively eliminating male brood. The proportion of haploid eggs produced by queens was close to 0.5 in late winter, decreased to less than 0.3 in spring and summer, and increased again to a value close to 0.5 in fall. Laboratory experiments indicate that temperture is a proximate factor influencing the primary sex ratio with a higher proportion of haploid eggs being laid at colder temperatures. Production of queen pupae ceased in mid-June, about three weeks before that of male pupae. After this time only worker pupae were produced. During the period of production of sexuals, the proportion of male pupae ranged from 0.30 to 0.38. Outside this period no males were reared although haploid eggs were produced all the year round by queens. Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens. The evolutionary significance of the production of male eggs by queens all the year round is as yet unclear. It may be a mechanism allowing queen replacement in the case of the death of the queens in the colony.

Role of bacterial biomass in the sorption of Ni by biomass-birnessite assemblages

Birnessites precipitated by bacteria are typically poorly crystalline Mn(IV) oxides enmeshed within biofilms to form complex biomass-birnessite assemblages. The strong sorption affinity of bacteriogenic birnessites for environmentally important trace metals is relatively well understood mechanistically, but the role of bacterial cells and extracellular polymeric substances appears to vary among trace metals. To assess the role of biomass definitively, comparison between metal sorption by biomass at high metal loadings in the presence and absence of birnessite is required. We investigated the biomass effect on Ni sorption through laboratory experiments utilizing the birnessite produced by the model bacterium, Pseudomonas putida. Surface excess measurements at pH 6?8 showed that birnessite significantly enhanced Ni sorption at high loadings (up to nearly 4-fold) relative to biomass alone. This apparent large difference in affinity for Ni between the organic and mineral components was confirmed by extended X-ray absorption fine structure spectroscopy, which revealed preferential Ni binding to birnessite cation vacancy sites. At pH >= 7, Ni sorption involved both adsorption and precipitation reactions. Our results thus support the view that the biofilm does not block reactive mineral surface sites; instead, the organic material contributes to metal sorption once high-affinity sites on the mineral are saturated.

Comparison of the methane oxidation rate in four media

Landfill gas emissions are one of the main sources of anthropogenic methane (CH4), a major greenhouse gas. In this paper, an economically attractive alternative to minimize greenhouse gas emissions from municipal solid waste landfills was sought. This alternative consists in special biofilters as landfill covers with oxidative capacity in the presence of CH4. To improve the quality/cost ratio of the project, compost was chosen as one of the cover substrates and soil (Typic red yellow-silt-clay Podzolic) as the other. The performance of four substrates was studied in laboratory experiments: municipal solid waste (MSW) compost, soil, and two soil-compost at different proportions. This study aimed to evaluate the suitability and environmental compatibility as a means of CH4 oxidation in biofilters. Four biofilters were constructed in 60 cm PVC tubes with an internal diameter of 10 cm. Each filter contained 2.3 L of oxidizing substrate at the beginning of the experiment. The gas used was a mixture of CH4 and air introduced at the bottom of each biofilter, at a flow of 150 mL min-1, by a flow meter. One hundred days after the beginning of the experiment, the best biofilter was the MSW compost with an oxidation rate of 990 g m-3 day-1 , corresponding to an efficiency of 44 %. It can be concluded that the four substrates studied have satisfactory oxidative capacity, and the substrates can be used advantageously as cover substrate of MSW landfills.

Chaotic, memory, and cooling rate effects in spin glasses: Evaluation of the Edwards-Anderson model

We investigate chaotic, memory, and cooling rate effects in the three-dimensional Edwards-Anderson model by doing thermoremanent (TRM) and ac susceptibility numerical experiments and making a detailed comparison with laboratory experiments on spin glasses. In contrast to the experiments, the Edwards-Anderson model does not show any trace of reinitialization processes in temperature change experiments (TRM or ac). A detailed comparison with ac relaxation experiments in the presence of dc magnetic field or coupling distribution perturbations reveals that the absence of chaotic effects in the Edwards-Anderson model is a consequence of the presence of strong cooling rate effects. We discuss possible solutions to this discrepancy, in particular the smallness of the time scales reached in numerical experiments, but we also question the validity of the Edwards-Anderson model to reproduce the experimental results.

Carbon and Nitrogen Mineralization in Soil Combining Sewage Sludge and Straw

ABSTRACT The combined incorporation of sewage sludge (SS) and oat straw (OS) to the soil can increase straw carbon mineralization and microbial nitrogen immobilization. This hypothesis was tested in two laboratory experiments, in which SS was incorporated in the soil with and without OS. One treatment in which only straw was incorporated and a control with only soil were also evaluated. The release of CO2 and mineral N in the soil after organic material incorporation was evaluated for 110 days. The cumulative C mineralization reached 30.1 % for SS and 54.7 % for OS. When these organic materials were incorporated together in the soil, straw C mineralization was not altered. About 60 % of organic N in the SS was mineralized after 110 days. This N mineralization index was twice as high as that defined by Resolution 375/2006 of the National Environmental Council. The combined incorporation of SS and OS in the soil caused an immobilization of microbial N of 5.9 kg Mg-1 of OS (mean 3.5 kg Mg-1). The results of this study indicated that SS did not increase straw C mineralization, but the SS rate should be adjusted to compensate for the microbial N immobilization caused by straw.

Detritivorous crustaceans become herbivores on jasmonate-deficient plants.

The jasmonate signal pathway is known to control defenses against herbivores, such as leaf eaters (folivores). Does the reach of the pathway extend to defense against other types of animal? Among the arthropods attracted to seed baits placed below flowering Arabidopsis thaliana plants are 2 largely nocturnal isopod crustaceans generally considered as detritivores: Porcellio scaber and Armadillidium vulgare. Parallel laboratory experiments identified the isopods as being capable of predation on intact plants. Isopod feeding was strongly facilitated in jasmonate-deficient Arabidopsis and rice plants. The feeding activity of isopods revealed potentially detritivore-sensitive, jasmonate-protected Achilles' heels in these architecturally different plants (petioles and inflorescence stems in Arabidopsis, and lower stem and mesocotyl in rice). The work addresses the question of what stops 2 detritivores from attacking living plants and provides evidence that it is, in part, the jasmonate signal pathway. Furthermore, senescent leaves from an Arabidopsis jasmonate mutant were consumed more rapidly than senescent wild-type leaves, suggesting that past activity of the jasmonate signal pathway in leaves may slow carbon recycling through detritivory.

On the spot damage detection methodology for highway bridges (tech transfer summary)

The objective of this work was to develop a low-cost portable damage detection tool to assess and predict damage areas in highway bridges. The proposed tool was based on standard vibration-based damage identification (VBDI) techniques but was extended to a new approach based on operational traffic load. The methodology was tested using numerical simulations, laboratory experiments, and field testing.

Perception and Interpretation of Advance Warning Signs on County Roads, HR-256, 1984

This research consisted of five laboratory experiments designed to address the following two objectives in an integrated analysis: (1) To discriminate between the symbol Stop Ahead warning sign and a small set of other signs (which included the word-legend Stop Ahead sign); and (2) To analyze sign detection, recognizability, and processing characteristics by drivers. A set of 16 signs was used in each of three experiments. A tachistoscope was used to display each sign image to a respondent for a brief interval in a controlled viewing experiment. The first experiment was designed to test detection of a sign in the driver's visual field; the second experiment was designed to test the driver's ability to recognize a given sign in the visual field; and the third experiment was designed to test the speed and accuracy of a driver's response to each sign as a command to perform a driving action. A fourth experiment tested the meanings drivers associated with an eight-sign subset of the 16 signs used in the first three experiments. A fifth experiment required all persons to select which (if any) signs they considered to be appropriate for use on two scale model county road intersections. The conclusions are that word-legend Stop Ahead signs are more effective driver communication devices than symbol stop-ahead signs; that it is helpful to drivers to have a word plate supplementing the symbol sign if a symbol sign is used; and that the guidance in the Manual on Uniform Traffic Control Devices on the placement of advance warning signs should not supplant engineering judgment in providing proper sign communication at an intersection.

Development of Self-Cleaning Box Culvert Design – Phase II, TR-619, 2013

Culverts are common means to convey flow through the roadway system for small streams. In general, larger flows and road embankment heights entail the use of multibarrel culverts (a.k.a. multi-box) culverts. Box culverts are generally designed to handle events with a 50-year return period, and therefore convey considerably lower flows much of the time. While there are no issues with conveying high flows, many multi-box culverts in Iowa pose a significant problem related to sedimentation. The highly erosive Iowa soils can easily lead to the situation that some of the barrels can silt-in early after their construction, becoming partially filled with sediment in few years. Silting can reduce considerably the capacity of the culvert to handle larger flow events. Phase I of this Iowa Highway Research Board project (TR-545) led to an innovative solution for preventing sedimentation. The solution was comprehensively investigated through laboratory experiments and numerical modeling aimed at screening design alternatives and testing their hydraulic and sediment conveyance performance. Following this study phase, the Technical Advisory Committee suggested to implement the recommended sediment mitigation design to a field site. The site selected for implementation was a 3-box culvert crossing Willow Creek on IA Hwy 1W in Iowa City. The culvert was constructed in 1981 and the first cleanup was needed in 2000. Phase II of the TR 545 entailed the monitoring of the site with and without the selfcleaning sedimentation structure in place (similarly with the study conducted in laboratory). The first monitoring stage (Sept 2010 to December 2012) was aimed at providing a baseline for the operation of the as-designed culvert. In order to support Phase II research, a cleanup of the IA Hwy 1W culvert was conducted in September 2011. Subsequently, a monitoring program was initiated to document the sedimentation produced by individual and multiple storms propagating through the culvert. The first two years of monitoring showed inception of the sedimentation in the first spring following the cleanup. Sedimentation continued to increase throughout the monitoring program following the depositional patterns observed in the laboratory tests and those documented in the pre-cleaning surveys. The second part of Phase II of the study was aimed at monitoring the constructed self-cleaning structure. Since its construction in December 2012, the culvert site was continuously monitored through systematic observations. The evidence garnered in this phase of the study demonstrates the good performance of the self-cleaning structure in mitigating the sediment deposition at culverts. Besides their beneficial role in sediment mitigation, the designed self-cleaning structures maintain a clean and clear area upstream the culvert, keep a healthy flow through the central barrel offering hydraulic and aquatic habitat similar with that in the undisturbed stream reaches upstream and downstream the culvert. It can be concluded that the proposed self-cleaning structural solution “streamlines” the area upstream the culvert in a way that secures the safety of the culvert structure at high flows while producing much less disturbance in the stream behavior compared with the current constructive approaches.

RFID Tags for Detecting Concrete Degradation in Bridge Decks, RB08-011, 2013

Steel reinforcing bar (rebar) corrosion due to chlorine ingress is the primary degradation mechanism for bridge decks. In areas where rock salt is used as a de-icing agent, salt water seeps into the concrete through cracks, causing corrosion of the rebar and potentially leading to catastrophic failure if not repaired. This project explores the use of radio frequency identification (RFID) tags as low-cost corrosion sensors. RFID tags, when embedded in concrete, will fail due to corrosion in the same manner as rebar after prolonged exposure to salt water. In addition, the presence of salt water interferes with the ability to detect the tags, providing a secondary mechanism by which this method can work. During this project, a fieldable RFID equipment setup was constructed and tested. In addition to a number of laboratory experiments to validate the underlying principles, RFID tags were embedded and tested in several actual bridge decks. Two major challenges were addressed in this project: issues associated with tags not functioning due to being in close proximity to rebar and issues associated with portland concrete coming in direct contact with the tags causing a detuning effect and preventing the tags from operating properly. Both issues were investigated thoroughly. The first issue was determined to be a problem only if the tags are placed in close proximity to rebar. The second issue was resolved by encapsulating the tag. Two materials, polyurethane spray foam and extruded polystyrene, were identified as providing good performance after testing, both in the lab and in the field.

Self-potentials in partially saturated media: the importance of explicit modeling of electrode effects

Self-potential (SP) data are of interest to vadose zone hydrology because of their direct sensitivity to water flow and ionic transport. There is unfortunately little consensus in the literature about how to best model SP data under partially saturated conditions, and different approaches (often supported by one laboratory data set alone) have been proposed. We argue that this lack of agreement can largely be traced to electrode effects that have not been properly taken into account. A series of drainage and imbibition experiments were considered in which we found that previously proposed approaches to remove electrode effects were unlikely to provide adequate corrections. Instead, we explicitly modeled the electrode effects together with classical SP contributions using a flow and transport model. The simulated data agreed overall with the observed SP signals and allowed decomposing the different signal contributions to analyze them separately. After reviewing other published experimental data, we suggest that most of them include electrode effects that have not been properly taken into account. Our results suggest that previously presented SP theory works well when considering the modeling uncertainties presently associated with electrode effects. Additional work is warranted to not only develop suitable electrodes for laboratory experiments but also to assure that associated electrode effects that appear inevitable in longer term experiments are predictable, so that they can be incorporated into the modeling framework.

Olfactory mediated interactions between Citrus aurantium Toxoptera citricida and Lysiphlebus testaceipes

The objective of this study was to establish whether there are olfactory interactions in the Lysiphlebus testaceipes Toxoptera citricida and Citrus aurantium tritrophic system. The response of male and female L. testaceipes to different odour sources of the host plant C. aurantium, the aphid host T. citricida and aphid-plant complex were investigated using a Y-tube olfactometer. Laboratory experiments were conducted by exposing individually aged male and female L. testaceipes to eight different odour treatments. Response of the parasitoids was taken after 15 min exposure to the volatiles from the different odour sources and based on their orientation to the particular chamber. Seventy percent of both male and female L. testaceipes showed high attractivity to aphid infested leaves. There was no significant difference based on age and sex of the parasitoid on their choice of odour. The organic compounds released by these combinations acted as semiochemicals in the tritrophic interactions and it is suggested that insect feeding induced attraction of the parasitoid L. testaceipes.

Development of In Situ Detection Methods for Materials-Related Distress (MRD) in Concrete Pavements: Phase 2, HR-1081, 2005

This project utilized information from ground penetrating radar (GPR) and visual inspection via the pavement profile scanner (PPS) in proof-of-concept trials. GPR tests were carried out on a variety of portland cement concrete pavements and laboratory concrete specimens. Results indicated that the higher frequency GPR antennas were capable of detecting subsurface distress in two of the three pavement sites investigated. However, the GPR systems failed to detect distress in one pavement site that exhibited extensive cracking. Laboratory experiments indicated that moisture conditions in the cracked pavement probably explain the failure. Accurate surveys need to account for moisture in the pavement slab. Importantly, however, once the pavement site exhibits severe surface cracking, there is little need for GPR, which is primarily used to detect distress that is not observed visually. Two visual inspections were also conducted for this study by personnel from Mandli Communications, Inc., and the Iowa Department of Transportation (DOT). The surveys were conducted using an Iowa DOT video log van that Mandli had fitted with additional equipment. The first survey was an extended demonstration of the PPS system. The second survey utilized the PPS with a downward imaging system that provided high-resolution pavement images. Experimental difficulties occurred during both studies; however, enough information was extracted to consider both surveys successful in identifying pavement surface distress. The results obtained from both GPR testing and visual inspections were helpful in identifying sites that exhibited materials-related distress, and both were considered to have passed the proof-of-concept trials. However, neither method can currently diagnose materials-related distress. Both techniques only detected the symptoms of materials-related distress; the actual diagnosis still relied on coring and subsequent petrographic examination. Both technologies are currently in rapid development, and the limitations may be overcome as the technologies advance and mature.

Optimization and Management of Materials in Earthwork Construction, TR-501, 2010

As a result of forensic investigations of problems across Iowa, a research study was developed aimed at providing solutions to identified problems through better management and optimization of the available pavement geotechnical materials and through ground improvement, soil reinforcement, and other soil treatment techniques. The overall goal was worked out through simple laboratory experiments, such as particle size analysis, plasticity tests, compaction tests, permeability tests, and strength tests. A review of the problems suggested three areas of study: pavement cracking due to improper management of pavement geotechnical materials, permeability of mixed-subgrade soils, and settlement of soil above the pipe due to improper compaction of the backfill. This resulted in the following three areas of study: (1) The optimization and management of earthwork materials through general soil mixing of various select and unsuitable soils and a specific example of optimization of materials in earthwork construction by soil mixing; (2) An investigation of the saturated permeability of compacted glacial till in relation to validation and prediction with the Enhanced Integrated Climatic Model (EICM); and (3) A field investigation and numerical modeling of culvert settlement. For each area of study, a literature review was conducted, research data were collected and analyzed, and important findings and conclusions were drawn. It was found that optimum mixtures of select and unsuitable soils can be defined that allow the use of unsuitable materials in embankment and subgrade locations. An improved model of saturated hydraulic conductivity was proposed for use with glacial soils from Iowa. The use of proper trench backfill compaction or the use of flowable mortar will reduce the potential for developing a bump above culverts.

Development of Self-Cleaning Box Culvert Designs, TR-545, 2009

The main function of a roadway culvert is to effectively convey drainage flow during normal and extreme hydrologic conditions. This function is often impaired due to the sedimentation blockage of the culvert. This research sought to understand the mechanics of sedimentation process at multi-box culverts, and develop self-cleaning systems that flush out sediment deposits using the power of drainage flows. The research entailed field observations, laboratory experiments, and numerical simulations. The specific role of each of these investigative tools is summarized below: a) The field observations were aimed at understanding typical sedimentation patterns and their dependence on culvert geometry and hydrodynamic conditions during normal and extreme hydrologic events. b) The laboratory experiments were used for modeling sedimentation process observed insitu and for testing alternative self-cleaning concepts applied to culverts. The major tasks for the initial laboratory model study were to accurately replicate the culvert performance curves and the dynamics of sedimentation process, and to provide benchmark data for numerical simulation validation. c) The numerical simulations enhanced the understanding of the sedimentation processes and aided in testing flow cases complementary to those conducted in the model reducing the number of (more expensive) tests to be conducted in the laboratory. Using the findings acquired from the laboratory and simulation works, self-cleaning culvert concepts were developed and tested for a range of flow conditions. The screening of the alternative concepts was made through experimental studies in a 1:20 scale model guided by numerical simulations. To ensure the designs are effective, performance studies were finally conducted in a 1:20 hydraulic model using the most promising design alternatives to make sure that the proposed systems operate satisfactory under closer to natural scale conditions.