Impact Resistance Behavior of Reinforced Concrete Beams Deteriorated due to Repeated Freezing and Thawing

Many existing reinforced concrete (RC) structures constructed more than 50 years ago now require maintenance. This is especially true in cold, snowy regions where significant frost damage deterioration of RC structures becomes a severe problem. In this study, falling-weight impact tests were performed to investigate the impact resistance behavior of RC beams degraded by frost damage. An RC beam was subjected to approximately 900 freeze-thaw cycles to emulate the frost damage before the execution of the impact test. The surface of the beam was remarkably scaled, and its coarse aggregate was exposed. The degree of deterioration was evaluated by the distribution of ultrasonic propagation velocity. The following conclusions were drawn. (1) The ultrasonic propagation velocity of RC beams was significantly reduced following 872 freeze-thaw cycles. At the upper edge of the RC beam, the ultrasonic wave propagation velocity decreased from 4,000 m/s to 1,500 m/s in some parts. This corresponds to a relative dynamic elastic modulus of approximately 14%. (2) The residual deflection of RC beams with frost damage increased at most by 20% compared with beams without frost damage. The increase in residual deflection was primarily related to the peeling of concrete at the collision site and the opening of multiple bending cracks. (3) According to the existing residual deflection calculation formula, an increase of 20% in the residual deflection corresponds to a decrease of about 17% in the bending capacity of the RC beam. When the relationship between the degree of frost damage deterioration and the impact resistance of RC structures is defined, existing structures subjected to accidental impact force from rockfalls are safer and can be maintained more efficiently

Turkestan Cockroaches Avoid Entering a Static Electric Field upon Perceiving an Attractive Force Applied to Antennae Inserted into the Field

This study analysed the mechanism of avoidance behaviour by adult Turkestan cockroaches (Shelfordella lateralis Walker) in response to a static electric field (S-EF) formed in the space between a negatively charged polyvinyl chloride-insulated iron plate (N-PIP) and a grounded metal net (G-MN). The negative surface charge supplied to the iron plate by a voltage generator caused the G-MN to polarise positively via electrostatic induction. In the S-EF, the negative charge of the N-PIP created a repulsive force that pushed free electrons in the field toward the ground via the G-MN. When insects released in the space surrounded by the S-EF inserted their antennae into the S-EF, they pulled them back reflexively and moved backward. The analysis indicated that an electric current flowed transiently toward the ground when an insect inserted its antennae into the S-EF. The insect became positively charged via this discharge and was attracted to the opposite pole (N-PIP). In response to this attractive force, the insect pulled its antennae back quickly. The positive electrification caused by the removal of free electrons from the antenna tip triggered the avoidance behaviour

Physical Methods for Electrical Trap-and-Kill Fly Traps Using Electrified Insulated Conductors

In the present study, we analyzed negative electricity released from insects captured by an electric field (EF)-producing apparatus. Adult houseflies (Musca domestica) were used as the model insect. The EF producer consisted of a negatively charged polyvinyl chloride membrane-insulated iron plate (N-PIP) and a non-insulated grounded iron plate (GIP) paralleled with the N-PIP. An EF was formed in the space between the plates. A housefly placed on the GIP was physically attracted to the N-PIP, and electricity released from the fly was detected as a specific transient electric current at the time of attraction and during subsequent confinement of the fly to the N-PIP. The magnitude of the insect-derived electric current became larger as the voltage applied to the N-PIP increased. We determined the total amount of electric current and confinement time within the apparatus necessary to kill all captured flies. These results demonstrate the insecticidal function and insect-capturing ability of the EF-producing apparatus

Developing a Phototactic Electrostatic Insect Trap Targeting Whiteflies, Leafminers, and Thrips in Greenhouses

Our aim was to develop an electrostatic apparatus to lure and capture silverleaf whiteflies (Bemisia tabaci), vegetable leafminers (Liriomyza sativae), and western flower thrips (Frankliniella occidentalis) that invade tomato greenhouses. A double-charged dipolar electric field producer (DD-EFP) was constructed by filling water in two identical transparent soft polyvinyl chloride tubes arrayed in parallel with fixed separation, and then, inserting the probes of grounded negative and positive voltage generators into the water of the two tubes to generate negatively and positively charged waters, respectively. These charged waters electrified the outer surfaces of the opposite tubes via dielectric polarization. An electric field formed between the oppositely charged tubes. To lure these phototactic insects, the water was colored yellow using watercolor paste, then introduced into the transparent insulator tubes to construct the yellow-colored DD-EFP. This apparatus lured insects in a manner similar to commercially available yellow sticky traps. The yellow-colored DD-EFP was easily placed as a movable upright screen along the plants, such that invading pests were preferentially attracted to the trap before reaching the plants. Furthermore, pests settling on the plants were attracted to the apparatus, which used a plant-tapping method to drive them off the plants. Our study provided an experimental basis for developing an electrostatic device to attract and capture insects that enter greenhouses

Efficient Use of the Green Fluorescence Protein Gene for Genetic Marking of Fusarium oxysporum f. sp. spinaciae

[Synopsis] To facilitate monitoring the infection behaviour of Fusarium oxysporum in planta, the hygromycinresistant gene and the green fluorescent protein gene were introduced into microconidia of F.oxysporum f. sp. spinaciae. The microconidia were subjected to high voltage pulse in the prescence of the plasmid for electroporation and the hygromycin-resistant transformants producing the green fluorescent protein were selected under UV irradiation. The integration of the marker genes into chromosomal DNA of these transformants was confiremed by polymerase chain reaction and Southern hybridization analysis. Transformation of phytopathogenic fungus with the green fluorescence gene enable us to easily and effectively detect the gene-marked fungi under UV-light without any additional chromogenic substrates for detecting translation product

An Electrostatic Pest Exclusion Strategy for Greenhouse Tomato Cultivation

Electrostatic devices generating an electric field (EF) are promising tools for greenhouse tomato cultivation. In these devices, an EF is generated in the space surrounding an insulated conductor (IC) that is charged by a voltage generator. Thus, a physical force is exerted on any insect that enters the EF, as a negatively charged IC (NC-IC) pushes a negative charge (free electrons) out of the insect body. The insect is polarized positively to be attracted to the NC-IC, and a grounded metal net (G-MN) repels the insect. This dual function of the apparatus (insect capture and repulsion) is the core of the electrostatic pest-exclusion strategy. In this study, we applied various innovative EF-based devices to evaluate their efficacy in greenhouse tomato cultivation. Our objective was to determine the optimal apparatus for simple, inexpensive construction by greenhouse workers. The results of this study will contribute to the development of sustainable pest-management protocols in greenhouse horticulture

Analysis of Pole-Ascending–Descending Action by Insects Subjected to High Voltage Electric Fields

The present study was conducted to establish an electrostatic-based experimental system to enable new investigations of insect behavior. The instrument consists of an insulated conducting copper ring (ICR) linked to a direct current voltage generator to supply a negative charge to an ICR and a grounded aluminum pole (AP) passed vertically through the center of the horizontal ICR. An electric field was formed between the ICR and the AP. Rice weevil (Sitophilus oryzae) was selected as a model insect due to its habit of climbing erect poles. The electric field produced a force that could be imposed on the insect. In fact, the negative electricity (free electrons) was forced out of the insect to polarize its body positively. Eventually, the insect was attracted to the oppositely charged ICR. The force became weaker on the lower regions of the pole; the insects sensed the weaker force with their antennae, quickly stopped climbing, and retraced their steps. These behaviors led to a pole-ascending–descending action by the insect, which was highly reproducible and precisely corresponded to the changed expansion of the electric field. Other pole-climbing insects including the cigarette beetle (Lasioderma serricorne), which was shown to adopt the same behavior