Protocol for using UV stimuli to evoke prey capture strikes in head-fixed zebrafish larvae.

Hunting in larval zebrafish begins with eye convergence and orienting turns, proceeds to approach swims, and ends with the strike, where larvae consume the prey. Here, we describe a protocol to present UV stimuli to zebrafish, which greatly increases the occurrence of hunting initiation and strikes. We also describe how we record and analyze strike behavior in head-fixed larvae. Our goals are to increase the robustness of prey capture and to allow other labs to implement the strike behavioral assay. For complete details on the use and execution of this protocol, please refer to Khan et al. (2023).1.

Zebrafish larvae use stimulus intensity and contrast to estimate distance to prey.

The ability to determine the distance to objects is an important feature of most visual systems, but little is known about the neuronal mechanisms for distance estimation. Larval zebrafish execute different visual behaviors depending on distance; at medium distances, they converge their eyes and approach, but when the prey is close enough, they execute a strike and suck the prey into their mouths. To study distance estimation, we developed a head-fixed strike assay. We found that we could evoke strike behavior in head-fixed larvae and quantify head movements to classify the behavior as a strike. Strikes were dependent on distance to prey, allowing us to use them to study distance estimation. Light intensity is rapidly attenuated as it travels through water, so we hypothesized that larvae could use intensity as a distance cue. We found that increasing stimulus intensity could cause larvae to strike at prey that would normally be out of range, and decreasing the intensity could lower the strike rate even for very proximal stimuli. In addition, stimulus contrast is a key parameter, and this could allow larvae to estimate distance over the range of natural illumination. Finally, we presented prey in the binocular vs. monocular visual field and found that monocular prey did evoke strikes, although the binocular input produced more. These results suggest that strike behavior is optimally evoked by bright UV dots in the binocular zone with minimal UV background light and provide a foundation to study the neuronal mechanisms of distance estimation.

Heavy Ion Displacement Damage Effect in Carbon Nanotube Field Effect Transistors.

Recent advances in carbon nanotube (CNT)-based integrated circuits have shown their potential in deep space exploration. In this work, the mechanism governing the heavy-ion-induced displacement damage (DD) effect in semiconducting single-walled CNT field effect transistors (FETs), which is one of the factors limiting device robustness in space, was first and thoroughly investigated. CNT FETs irradiated by a Xe ion fluence of 1012 ions/cm2 can maintain a high on/off current ratio, while transistors' performance failure is observed as the ion fluence increased to 5 × 1012 ions/cm2. Controllable experiments combined with numerical simulations revealed that the degradation mechanism changed as the nonionizing radiation energy built up. The trap generation in the gate dielectric, instead of the CNT channel, was identified as the dominating factor for the high-energy-radiation-induced device failure. Therefore, CNT FETs exhibited a >10× higher DD tolerance than that of Si devices, which was limited by the channel damage under irradiation. More importantly, the distinct failure mechanism determined that CNT FETs can maintain a high DD tolerance of 2.8 × 1013 MeV/g as the technology node scales down to 45 nm node, suggesting the potential of CNT-based VLSI for high-performance and high-robustness space applications.

Estimating the non-linear effects of urban built environment at residence and workplace on carbon dioxide emissions from commuting.

Understanding the relationship between CO2 emissions from commuting (CEC) and the built environment is crucial for sustainable transportation and land-use policymaking during the process of constructing a low carbon city. Previous studies usually assume that the relationship is linear, which may lead to inaccurate CEC prediction and ineffective policy. Using daily travel survey data of residents in the central city of Jinan, this study adopted a gradient boosting decision tree model to explore the threshold effect and the non-linear relationship between built environments and CEC. Our findings suggest that 40% of CEC is related to the workplace environment, which is higher than the residential environment and other socioeconomic variables. The five most important variables are road density within 1 km radius of the workplace (13.493%), distance to the center at workplace and residence (10.908%, 10.530%), population density at workplace (9.097%) and distance to bus stop from the residence (8.399%). Distance to city center plays the most important role and its non-linear relationship reflects the influence of the urban spatial structure of Jinan on CEC. Furthermore, the thresholds and non-linear relationships provide planning guidelines to support urban planning development policies for low carbon city.

Robustness and plasticity in Drosophila heat avoidance.

Simple innate behavior is often described as hard-wired and largely inflexible. Here, we show that the avoidance of hot temperature, a simple innate behavior, contains unexpected plasticity in Drosophila. First, we demonstrate that hot receptor neurons of the antenna and their molecular heat sensor, Gr28B.d, are essential for flies to produce escape turns away from heat. High-resolution fly tracking combined with a 3D simulation of the thermal environment shows that, in steep thermal gradients, the direction of escape turns is determined by minute temperature differences between the antennae (0.1°-1 °C). In parallel, live calcium imaging confirms that such small stimuli reliably activate both peripheral thermosensory neurons and central circuits. Next, based on our measurements, we evolve a fly/vehicle model with two symmetrical sensors and motors (a "Braitenberg vehicle") which closely approximates basic fly thermotaxis. Critical differences between real flies and the hard-wired vehicle reveal that fly heat avoidance involves decision-making, relies on rapid learning, and is robust to new conditions, features generally associated with more complex behavior.