真空容器内でのシリカダスト浮遊の実験的研究およびマイクロキャビティ内での帯電と表面電界によって浮遊する月砂高度の予測

There is a soil-like layer above the bedrock of the Moon that is produced by the small meteoroid impacts on the lunar surface, which is also called as the lunar regolith. The size of the regolith particles ranges from several centimeters to submicron size, and the small-scale particles are also referred as the lunar dust, which can be transported by the electrostatic forces above the lunar surface. Electrostatically lofted and/or levitated dust grains were detected while scattering the sunlight above the lunar terminator region, and this physical phenomenon has been called the lunar horizon glow (LHG). TV cameras of Surveyor missions first monitored the LHG in 1966 and 1968, and the excessive brightness to coronal and zodiacal light (CZL) indicated that the dust population was considerably denser than the levels that can be produced by micrometeorite ejecta on the lunar surface. In addition, all observations of the LHG were under the solar wind plasma, and the lunar surface directly interacts with the charged particles in the absence of a global magnetic field and a dense atmosphere. Even though the solar wind plasma has a lower temperature and higher density than the magnetospheric plasma, enhanced fluxes of charged particles can be observed in some cases such as solar energetic particle events or coronal mass ejections (CMEs). In this research, the purpose can be described as (1) predicting the maximum height variation of the dust grains above the lunar terminator under various ambient plasma conditions and (2) experimentally investigating the silica dust lofting in the vacuum chamber under the electron beam. Therefore, the equations that are used in the simulations are compared to the experimental results, and the significance of the surface parameters such as the presence of the horizontal electric field and the increased packing density on the electrostatical dust launching are investigated as well. The LHG observations, the lunar dust exosphere measurements, and the previous studies on the lunar dust simulations and experiments are presented in chapter 1. In addition, the simulation method of the lunar surface charging and the results of the surface potential, the electric field and Debye length are discussed for the plasma parameters of the regular solar wind and three selected geoeffective CME events in chapter 2. In chapter 3, the initial separation of the dust particles and the maximum height calculations are presented in detail. The simulation results show that the surface potential is highly variable on the lunar terminator region, and the dust launching rates are significantly controlled by the secondary electron emission and the dust sizes. Even though the micron-sized dust grains are launched from the surface more frequently than the submicron-sized dust particles, their heights are less influenced by the surface electric field in all cases. The simulations are performed for the dust particles with 0.1, 1 and 5 μm radius, and the uncertainty range of the height predictions are represented as well. In chapter 4, the experiments on the silica dust grains are explained in detail. The experiments are performed under 4×10-3 Pa pressure in a general-purpose vacuum chamber. In addition, an electron beam is produced from a cathode ray tube, and the electron current density is measured as approximately 2.87×10-4 Am-2. Different from the previous dust lofting experiments, the initial launching velocities of the grains are detected by the microscopic telescope and the high-speed camera by focusing on the near-surface area above the dust sample. Three different types of experiments are performed on the silica dust grains. First, the dust grains are loaded on the graphite plate without applying additional pressure or external horizontal electric field during the experiment. Therefore, it is called the simple case, and the measurements are compared with the estimated values. Second, the separate dust samples are compressed after loading on to the graphite plate with approximately 781 and 3780 Pa in order to increase the contact surface areas among the dust grains while decreasing the number of the microcavities. Third, the graphite plate is placed between two parallel aluminum plates that are separated by 5 and 12 cm distance and biased to 240 V in both cases. Therefore, it is expected to increase the number of the rolling particles over the surface while increasing the number of the inter-particle collisions. Finally, all of the results are discussed for the simulations and the experiments in chapter 5. First, the dust grains with 5 μm radius reach significantly similar heights with the LHG observations of Surveyor mission in the simulations. Second, the dust grains 0.1 μm in radius are lofted to the heights similar to the Lunokhod-2 astrophotometer observations under the regular solar wind. Third, the laboratory experiments point out that several factors are determinative to estimate the dust lofting such as the contact surface areas between the dust grains, the packing density, the existence of the microcavities, and the inter-particle collisions in the presence of the horizontal electric field. Most of the particles are launched within the estimated range for the simple case. Furthermore, increased packing density reduces the number of the lofted dust grains; however, their vertical launching velocities are increased due to stronger electrostatic potential energy built-up between the dust grains. In addition, strong horizontal electric field contributes to the dust release from the surface by potentially increasing the inter-particle collisions; and the current results suggest lower launching velocities than the previous cases. Finally, the aggregates are lofted as well as the single particles, and some of them separated during the lofting motion. Therefore, the separation of charged dust grains on the flight can be an additional source for the smaller grains. In chapter 6, the conclusions and the recommendations are explained, and the future tasks are determined as the investigation of the correlation between the micrometeorite impact regions and the electrostatic transportation of the dust grains.九州工業大学博士学位論文 学位記番号：工博甲第460号 学位授与年月日：平成30年9月21日1 INTRODUCTION|2 LUNAR SURFACE CHARGING SIMULATIONS|3 ELECTROSTATIC LUNAR DUST TRANSPORTATION|4 EXPERIMENTAL INVESTIGATION ON SILICA DUST LOFTING|5 DISCUSSION|6 CONCLUSIONS AND RECOMMENDATIONS九州工業大学平成30年

真空容器内でのシリカダスト浮遊の実験的研究およびマイクロキャビティ内での帯電と表面電界によって浮遊する月砂高度の予測

九州工業大学博士学位論文（要旨）学位記番号：工博甲第460号 学位授与年月日：平成30年9月21

Mangroves, fisheries and community livelihoods

Mangroves are thought to provide vital ecosystem services to coastal fishing communities through the enhancement of fisheries production. Ongoing loss of mangrove extent globally is therefore of societal concern given that communities living near mangroves rely on mangrove-fishing for income and subsistence. Whilst research and conservation efforts have successfully advocated mangrove restoration, and promoted the importance of mangroves in climate mitigation and coastal protection, knowledge of how people use mangroves for fishing is less well developed (Chapters 1 and 2). To date, most quantitative estimates of the value of the presence of mangroves to fishing have been limited to single fishing sectors, gear types or species groups and therefore fail to capture the full diversity of fishing practices, and thus the true socio-economic benefits of mangrove-fishing. The thesis first develops a definition of what mangrove-fisheries can encompass. A case study which investigated the fishing activities associated with mangroves through interviews with fishers was conducted in the Perancak Estuary, Bali, Indonesia. A framework based on this case study was developed as a flexible tool for identifying the characteristics of a mangrove-fishery in a local context (Chapter 3). Using this framework, Chapter 4 measured the all-encompassing value of mangrove benefits to fishing in the Peam Krasaop Fishing Community (PKFC), Koh Kong Province, southwest Cambodia. The ecosystem service value of mangroves for fishing to households in the PKFC was arrived at using daily landings volumes and market values provided through interview surveys with fishers. Both chapters highlight the highly diverse nature of mangrove-fisheries. To what extent are the benefits of mangrove purely local phenomena or are these benefits reflected in global catch datasets? Chapter 5 investigates the spatial relationships between mangrove extent and fisheries catches at the global scale. For the period 2000-2012, small-scale (artisanal and subsistence) catch data, from the Sea Around Us fisheries catch database, was matched against high resolution mangrove extent maps from the Global Database of Continuous Mangrove Forest Cover for the 21st Century revealing that contrary to much of the previous literature, variation in mangrove-associated species catches is better explained by proximity to the mangrove than by mangrove area. Finally, Chapter 6 considers how new and emergent technologies, such as real-time vessel tracking, are likely to improve our ability to estimate mangrove-fishery value, assesses the potential of restored mangroves in providing ecosystem services, and reflects on how communities will need to respond to pressures on mangrove-fishery livelihoods from global environmental change.  This PhD was funded by the Nippon Foundation Nereus Program

Control of Visually Guided Behavior by Distinct Populations of Spinal Projection Neurons

A basic question in the field of motor control is how different actions are represented by activity in spinal projection neurons. We used a new behavioral assay to identify visual stimuli that specifically drive basic motor patterns in zebrafish. These stimuli evoked consistent patterns of neural activity in the neurons projecting to the spinal cord, which we could map throughout the entire population using in vivo two-photon calcium imaging. We found that stimuli that drive distinct behaviors activated distinct subsets of projection neurons, consisting, in some cases, of just a few cells. This stands in contrast to the distributed activation seen for more complex behaviors. Furthermore, targeted cell by cell ablations of the neurons associated with evoked turns abolished the corresponding behavioral response. This description of the functional organization of the zebrafish motor system provides a framework for identifying the complete circuit underlying a vertebrate behavior.Molecular and Cellular Biolog

Sustained Rhythmic Brain Activity Underlies Visual Motion Perception in Zebrafish.

Following moving visual stimuli (conditioning stimuli, CS), many organisms perceive, in the absence of physical stimuli, illusory motion in the opposite direction. This phenomenon is known as the motion aftereffect (MAE). Here, we use MAE as a tool to study the neuronal basis of visual motion perception in zebrafish larvae. Using zebrafish eye movements as an indicator of visual motion perception, we find that larvae perceive MAE. Blocking eye movements using optogenetics during CS presentation did not affect MAE, but tectal ablation significantly weakened it. Using two-photon calcium imaging of behaving GCaMP3 larvae, we find post-stimulation sustained rhythmic activity among direction-selective tectal neurons associated with the perception of MAE. In addition, tectal neurons tuned to the CS direction habituated, but neurons in the retina did not. Finally, a model based on competition between direction-selective neurons reproduced MAE, suggesting a neuronal circuit capable of generating perception of visual motion

A retinal circuit generating a dynamic predictive code for oriented features

Sensory systems must reduce the transmission of redundant information to function efficiently. One strategy is to continuously adjust the sensitivity of neurons to suppress responses to common features of the input while enhancing responses to new ones. Here we image the excitatory synaptic inputs and outputs of retinal ganglion cells to understand how such dynamic predictive coding is implemented in the analysis of spatial patterns. Synapses of bipolar cells become tuned to orientation through presynaptic inhibition generating lateral antagonism in the orientation domain. Individual ganglion cells receive excitatory synapses tuned to different orientations but feedforward inhibition generates a high-pass filter that only transmits the initial activation of these inputs, thereby removing redundancy. These results demonstrate how a dynamic predictive code can be implemented by circuit motifs common to many parts of the brain

Whole-Brain Activity Maps Reveal Stereotyped, Distributed Networks for Visuomotor Behavior

Most behaviors, even simple innate reflexes, are mediated by circuits of neurons spanning areas throughout the brain. However, in most cases, the distribution and dynamics of firing patterns of these neurons during behavior are not known. We imaged activity, with cellular resolution, throughout the whole brains of zebrafish performing the optokinetic response. We found a sparse, broadly distributed network that has an elaborate but ordered pattern, with a bilaterally symmetrical organization. Activity patterns fell into distinct clusters reflecting sensory and motor processing. By correlating neuronal responses with an array of sensory and motor variables, we find that the network can be clearly divided into distinct functional modules. Comparing aligned data from multiple fish, we find that the spatiotemporal activity dynamics and functional organization are highly stereotyped across individuals. These experiments systematically reveal the functional architecture of neural circuits underlying a sensorimotor behavior in a vertebrate brain.Molecular and Cellular Biolog

Perception of Fourier and non- Fourier motion by larval zebrafish

articles Zebrafish larvae innately begin responding to moving stimuli shortly after hatching. In their optomotor response, which is elicited by large moving stimuli presented from below or the side 1,2 , larvae swim in the direction of perceived motion. The distance they travel in a given time indicates the effectiveness of the stimulus. By observing the response of many larvae to computer-animated displays, we could determine which attributes of a moving stimulus the zebrafish visual system detects. If luminance-defined features drift smoothly or jump in space, they can produce strong sensations of motion. A number of proposed models explain how motion information can be extracted. In a simple model, a point-to-point comparison is made between the luminance pattern and a spatially displaced copy of the pattern that was seen a short time before 3 . The displacement that gives the best fit tells the brain the direction and speed of movement. A more complex strategy is to look at the Fourier motion energy in the visual scene Although there is evidence that humans can use both feature matching and motion energy to detect movement 7 , they may also sense motion when presented with stimuli in which only secondorder features such as contrast, texture or flicker are moving Here we find that the fish larvae detect moving features of visu- A moving grating elicits innate optomotor behavior in zebrafish larvae; they swim in the direction of perceived motion. We took advantage of this behavior, using computer-animated displays, to determine what attributes of motion are extracted by the fish visual system. As in humans, first-order (luminance-defined or Fourier) signals dominated motion perception in fish; edges or other features had little or no effect when presented with these signals. Humans can see complex movements that lack first-order cues, an ability that is usually ascribed to higher-level processing in the visual cortex. Here we show that second-order (non-Fourier) motion displays induced optomotor behavior in zebrafish larvae, which do not have a cortex. We suggest that second-order motion is extracted early in the lower vertebrate visual pathway. al stimuli in a way that is qualitatively similar to humans: both firstorder and second-order cues drive their behavioral response. Our demonstration of second-order motion detection in fish challenges the idea that higher-level, cortical mechanisms are necessary to explain this capacity of the visual system. RESULTS Optomotor responses to Fourier motion The assay used to measure optomotor responses is similar to the one described previously 2 (Methods). Movies showing drifting gratings evoke strong optomotor responses in almost all fish in a clutch. Fish do not respond to a moving grating with a stripe width narrower than approximately 9°, which is slightly less than the predicted resolution limit of the larval cone mosaic, 6°at this age In the following experiments, responses were normalized to the effect of a designated strong stimulus, a 100% contrast square wave subtending 100°of visual angle per cycle and moving at 1 Hz for 30 seconds Although the fish seemed to follow a motion signal in the movies, it was possible that they were tracking features such as light or dark regions or edges that were being displaced. We did an experiment to show that the optomotor response is truly a response to motion. A motion display was shown of a sine wave grating tha

The Tangential Nucleus Controls a Gravito-inertial Vestibulo-ocular Reflex

Whilst adult vertebrates sense changes in head position using two classes of accelerometer, at larval stages zebrafish lack functional semicircular canals and rely exclusively on their otolithic organs to transduce vestibular information. Despite this limitation, they perform an effective vestibulo-ocular reflex (VOR) that serves to stabilize gaze in response to pitch and roll tilts. Using single-cell electroporations and targeted laser-ablations, we identified a specific class of central vestibular neurons, located in the tangential nucleus, which are essential for the utricle-dependent VOR. Tangential nucleus neurons project contralaterally to extraocular motoneurons, and in addition, to multiple sites within the reticulospinal complex. We propose that tangential neurons function as a broadband inertial accelerometer, processing utricular acceleration signals to control the activity of extraocular and postural neurons, thus completing a fundamental three-neuron circuit responsible for gaze stabilization.Molecular and Cellular Biolog