OIST Institutional Repository
Not a member yet
2744 research outputs found
Sort by
Defining raft domains in the plasma membrane
Get PDFMany plasma membrane (PM) functions depend on the cholesterol concentration in the PM in strikingly nonlinear, cooperative ways: fully functional in the presence of physiological cholesterol levels (35~45 mol%), and nonfunctional below 25 mol% cholesterol; namely, still in the presence of high concentrations of cholesterol. This suggests the involvement of cholesterol-based complexes/domains formed cooperatively. In this review, by examining the results obtained by using fluorescent lipid analogs and avoiding the trap of circular logic, often found in the raft literature, we point out the fundamental similarities of liquid-ordered (Lo)-phase domains in giant unilamellar vesicles, Lo-phase-like domains formed at lower temperatures in giant PM vesicles, and detergent-resistant membranes: these domains are formed by cooperative interactions of cholesterol, saturated acyl chains, and unsaturated acyl chains, in the presence of >25 mol% cholesterol. The literature contains evidence, indicating that the domains formed by the same basic cooperative molecular interactions exist and play essential roles in signal transduction in the PM. Therefore, as a working definition, we propose that raft domains in the PM are liquid-like molecular complexes/domains formed by cooperative interactions of cholesterol with saturated acyl chains as well as unsaturated acyl chains, due to saturated acyl chains' weak multiple accommodating interactions with cholesterol and cholesterol's low miscibility with unsaturated acyl chains and TM proteins. Molecules move within raft domains and exchange with those in the bulk PM. We provide a logically established collection of fluorescent lipid probes that preferentially partition into raft and non-raft domains, as defined here, in the PM.journal articl
Magneto-Oscillations and Anomalous Current States in a Photoexcited Electron Gas on Liquid Helium
No full textjournal articl
Interface engineering strategies towards Cs2AgBiBr6 single-crystalline photodetectors with good Ohmic contact behaviours
Get PDFLead-free double perovskite materials have attracted much interest for optoelectronic applications due to their nontoxicity and high stability. In this work, centimetre-sized Cs2AgBiBr6 single crystals were successfully grown using methylammonium bromide (MABr) as the flux by a top-seeded solution growth (TSSG) method. The low-temperature crystal structure of Cs2AgBiBr6 single crystals was determined and refined. To investigate the interface problems between Cs2AgBiBr6 single crystals and electrodes, the optical band gap, X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements were performed on Cs2AgBiBr6 single crystals. More importantly, we investigated the photodetectors based on Cs2AgBiBr6 single crystals with different contact electrodes (Au, Ag, and Al). It is found that a good Ohmic contact with Ag electrodes enables excellent photo-response behaviors. Furthermore, we studied the photodetectors based on Cs2AgBiBr6 single crystals using Ag electrodes under room and low temperature conditions, which underwent phase transition. Cs2AgBiBr6 single crystal photodetectors show clear differences at room and low temperatures, which is caused by the work function changes of Cs2AgBiBr6 single crystals induced by the reversible phase transition. These attractive properties may enable opportunities to apply emerging double perovskite single-crystalline materials for high-performance optoelectronic devices.journal articl
Wasabi versus red imported fire ants: preliminary test of repellency of microencapsulated allyl isothiocyanate against Solenopsis invicta (Hymenoptera: Formicidae) using bait traps in Taiwan
Get PDFSea container has been identified as a major pathway for the unintended entry and spread of alien ant species. In Japan, red imported fire ants, Solenopsis invicta Buren (Hymenoptera: Formicidae), which are among the most harmful alien ants, were first detected in a shipping container from China in May 2017, and the invasion into Japan via the trade pathway is still continuing. To prevent containers contaminated with S. invicta and its establishment in Japan, control measures, such as repellents, are urgently required. The present study is the first to evaluate repellency of microencapsulated allyl isothiocyanate (AITC) against S. invicta, as a preliminary step to use the innovative equipment for invasive species management in sea containers. In a field in Taiwan heavily infested with S. invicta, a repellent test of microencapsulated AITC using bait traps showed that the equipment completely prevents S. invicta from accessing the bait. Due to its volatility and irritancy, AITC, a safe natural repellant in wasabi (Eutrema japonicum (Miq.) Kiudz), has not been used for pest management in containerized cargo. However, the encapsulation of AITC solves this problem by allowing controlled vapor release. Microencapsulated AITC has considerable potential as an effective measure to stop the spread of S. invicta through global trade.journal articl
Serotonergic Control of Brain-Wide Dynamics
Get PDFOkinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophySerotonin, one of the neuromodulators, is associated with multiple functions, such as the wake-sleep cycle, decision making, and mood. Serotonin is also the primary tar-get of medication for major depression (MD), notably by selective serotonin re-uptake inhibitors (SSRIs). However, it is widely known that serotonergic antidepressants re-quire long-term administration, and acute medication sometimes worsens symptoms.Serotonergic regulation of brain-wide dynamics remains crucial for understanding its roles in behavioral and cognitive functions as well as the mechanism of antidepressant medication. First, I studied the influences of a serotonergic antidepressant on brain dynamics with functional magnetic resonance imaging in rodents. I found that the functional connectivity between the bed nucleus of steria terminalis (BST) and the ventral retrosplenial cortex (vRSC) distinctively responded to acute serotonergic antidepressant treatment, escitalopram. Additionally, long-term serotonergic antidepressant treatment promoted spontaneous locomotion and influenced anxiety like behaviors only in context-dependent and individually variable ways. The results imply that long-term serotonergic antidepressant treatment enhances intrinsic motivation,but not anxiety. Additionally, I analyzed large-scale brain dynamics with functional connectivity analysis and energy landscape analysis (ELA). My ELA analysis revealed that chronic administration of serotonergic antidepressants maintained dynamic brain states linking major attractor states, while conventional functional connectivity (FC)analysis did not show any difference caused by serotonergic antidepressants. The intermediate brain states, which are supported by modular integration, are associated with active exploration. My findings suggest that serotonergic antidepressants induce resilience by stabilizing brain state dynamics as a result of shaping functional network architecture. In the second study, I conducted a pilot experiment to assess serotonergic modulation of brain dynamics by optogenetic stimulation of serotonin neurons in the dorsal raphe nucleus (DRN). In the first animal test, I found brain responses in the frontal cortical regions (the anterior cingulate cortex, the medial prefrontal cortex, and the insular cortex), the striatum, and the ventral tegmental area (VTA). In a reward delay task, optogenetic activation of DRN serotonin neurons enhanced waiting for delayed rewards, which confirmed the effectivenss of optogenetic stimulation. The result suggested the feasibility of studying serotonergic modulation with opto-fMRI. My thesis delineates how the serotonergic system regulates brain-wide dynamics at short- and long-term scales.doctoral thesi
State engineering in one-dimensional quantum gases
Get PDFOkinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyThe development of quantum technologies requires the understanding, controlling and engineering of quantum states of interacting systems, a challenge currently driven by experimental progress. In this work I study, both analytically and numerically, two specific models of one-dimensional ultracold atomic systems to determine their states and accessible dynamical behaviour. The first part of the work deals with the creation of a bosonic atom dispenser, a tool which would allow to deterministically separate any number of atoms from an interacting ultracold gas or create a many-particle noon state. By engineering an effectively three-level system, I show that a robust adiabatic process exists that connects the initial and target Fock states. Moreover, I demonstrate its potential to be experimentally implemented using radio-frequency traps. In the second part, I derive an analytical single-particle solution for the arbitrary finite Kronig–Penney model. In this model the atoms are trapped in an infinite square well which contains an arbitrary number of arbitrarily positioned point-like barriers of arbitrary heights. I also demonstrate that using certain parameters in the model as extra (virtual) dimensions one can observe the emergence of higher-dimensional physics in this one-dimensional system. In particular, I show the appearance of edge states and the emergence of a Hofstadter butterfly-like momentum spectrum in various configurations of the model. Finally, using the single-particle solutions, I study many-body correlations in a gas of either infinitely repulsive bosons or non-interacting fermions.doctoral thesi
Diverse metabolic reactions activated during 58-hr fasting are revealed by non-targeted metabolomic analysis of human blood
Get PDFDuring human fasting, metabolic markers, including butyrates, carnitines, and branched-chain amino acids, are upregulated for energy substitution through gluconeogenesis and use of stored lipids. We performed non-targeted, accurate semiquantitative metabolomic analysis of human whole blood, plasma, and red blood cells during 34-58 hr fasting of four volunteers. During this period, 44 of ~130 metabolites increased 1.5~60-fold. Consistently fourteen were previously reported. However, we identified another 30 elevated metabolites, implicating hitherto unrecognized metabolic mechanisms induced by fasting. Metabolites in pentose phosphate pathway are abundant, probably due to demand for antioxidants, NADPH, gluconeogenesis and anabolic metabolism. Global increases of TCA cycle-related compounds reflect enhanced mitochondrial activity in tissues during fasting. Enhanced purine/pyrimidine metabolites support RNA/protein synthesis and transcriptional reprogramming, which is promoted also by some fasting-related metabolites, possibly via epigenetic modulations. Thus diverse, pronounced metabolite increases result from greatly activated catabolism and anabolism stimulated by fasting. Anti-oxidation may be a principal response to fasting.journal articl
Comparative transcriptomics of social insect queen pheromones
Get PDFQueen pheromones are chemical signals that mediate reproductive division of labor in eusocial animals. Remarkably, queen pheromones are composed of identical or chemically similar compounds in some ants, wasps and bees, even though these taxa diverged > 150MYA and evolved queens and workers independently. Here, we measure the transcriptomic consequences of experimental exposure to queen pheromones in workers from two ant and two bee species (genera: Lasius, Apis, Bombus), and test whether they are similar across species. Queen pheromone exposure affected transcription and splicing at many loci. Many genes responded consistently in multiple species, and the set of pheromone-sensitive genes was enriched for functions relating to lipid biosynthesis and transport, olfaction, production of cuticle, oogenesis, and histone (de)acetylation. Pheromone-sensitive genes tend to be evolutionarily ancient, positively selected, peripheral in the gene coexpression network, hypomethylated, and caste-specific in their expression. Our results reveal how queen pheromones achieve their effects, and suggest that ants and bees use similar genetic modules to achieve reproductive division of labor.journal articl
Heterogeneous flow inside threads of low viscosity fluids leads to anomalous long filament lifetimes
Get PDFFormation and breakup of fluid threads is pervasive in nature and technology, where high extensibility of fluid filaments and extended filament lifetimes are commonly observed as a consequence of fluid viscoelasticity. In contrast, threads of low viscous Newtonian fluids like water rupture quickly. Here, we demonstrate that a unique banding instability during filament thinning of model surfactant solutions, with a viscosity close to water and no measurable elasticity, leads to extremely long filament lifetimes and to the formation of remarkably long threads. Complementary measurements in planar extension as well as in shear reveal that this flow instability is characterized by a multivalued stress, arising beyond a critical strain rate, irrespective of flow kinematics. Our work reports the first observation of such phenomena during extensional deformation and provides a unifying view on instabilities in complex flow fields.journal articl
Draculab: A Python Simulator for Firing Rate Neural Networks With Delayed Adaptive Connections
Get PDFDraculab is a neural simulator with a particular use scenario: firing rate units with delayed connections, using custom-made unit and synapse models, possibly controlling simulated physical systems. Draculab also has a particular design philosophy. It aims to blur the line between users and developers. Three factors help to achieve this: a simple design using Python's data structures, extensive use of standard libraries, and profusely commented source code. This paper is an introduction to Draculab's architecture and philosophy. After presenting some example networks it explains basic algorithms and data structures that constitute the essence of this approach. The relation with other simulators is discussed, as well as the reasons why connection delays and interaction with simulated physical systems are emphasized.journal articl