OIST Institutional Repository
Not a member yet
2744 research outputs found
Sort by
Charge transfer dynamics in conjugated polymer/MoS2 organic/2D heterojunctions
Get PDFHeterojunctions between organic and two-dimensional (2D) semiconductors show promising applications in ultrathin electronic and optoelectronic devices, including field-effect transistors, light-emitting diodes, and photovoltaics. These organic/2D heterojunctions form ideal interfaces due to the lack of dangling bonds at the surfaces of the neat (i.e., individual) materials and their propensity to interact via van der Waals forces. Despite this, organic/2D heterojunction devices have had relatively low quantum efficiencies, suggesting limitations on the charge transport within these devices. Understanding the charge transfer dynamics across organic/2D semiconductor interfaces at fundamental time scales is an important part of overcoming these limitations. In this work, we investigate the photoexcited charge carrier dynamics in organic/2D heterojunctions comprised of large-area monolayer MoS2 and solution-deposited organic semiconducting conjugated polymer thin-films. Using photoluminescence and femtosecond transient absorption spectroscopy, we compare the efficiencies of charge transfer for three different conjugated polymer/MoS2 heterojunctions: P3HT, PCDTBT, and PTB7. We show that electron transfer occurs from MoS2 to P3HT in under 9 ps, and from MoS2 to PCDTBT or PTB7 in under 120 fs. Despite this, we demonstrate that the P3HT/MoS2 heterojunction is the most efficient because the transferred charges have an order-of-magnitude increase in their lifetimes, giving rise to enhanced photoluminescence. This work will help guide designs of future organic/2D heterojunctions using scalable fabrication technologies.journal articl
Statistical analysis of electronic and phononic transport simulations of metallic atomic contacts
Get PDFWe adapt existing phonon heat transport methods to compute the phononic thermal conductance of metallic atomic contacts during a stretching process. Nonequilibrium molecular dynamics simulations are used to generate atomic configurations and to simultaneously determine the phononic thermal conductance. Combining the approach with established electronic structure calculations based on a tight-binding parametrization allows us to calculate in addition charge transport properties of each contact geometry within the Landauer-Büttiker formalism. The method is computationally fast enough to perform a statistical analysis of many stretching events, and we apply it here to atomic junctions formed from three different metals, namely gold (Au), platinum (Pt), and aluminum (Al). The description of both phononic and electronic contributions to heat transport allows us to examine the validity of the Wiedemann-Franz law at the atomic scale. We find that it is well obeyed in the contact regime at room temperature for Au and Al as far as only electronic contributions are concerned, but deviations of up to 10% arise for Pt. If the total thermal conductance is studied, deviations of typically less than 10% arise for Au and Al, which can be traced back mainly to phononic contributions to the thermal conductance, while electronic and phononic contributions can add up to some 20% for single-atom contacts of Pt.journal articl
Integral fluctuation relations for entropy production at stopping times
Get PDFA stopping time T is the first time when a trajectory of a stochastic process satisfies a specific criterion. In this paper, we use martingale theory to derive the integral fluctuation relation = 1 for the stochastic entropy production S-tot in a stationary physical system at stochastic stopping times T. This fluctuation relation implies the law >= 0, which states that it is not possible to reduce entropy on average, even by stopping a stochastic process at a stopping time, and which we call the second law of thermodynamics at stopping times. This law bounds the average amount of heat and work a system can extract from its environment when stopped at a random time. Furthermore, the integral fluctuation relation implies that certain fluctuations of entropy production are universal or are bounded by universal functions. These universal properties descend from the integral fluctuation relation by selecting appropriate stopping times: for example, when T is a first-passage time for entropy production, then we obtain a bound on the statistics of negative records of entropy production. We illustrate these results on simple models of nonequilibrium systems described by Langevin equations and reveal two interesting phenomena. First, we demonstrate that isothermal mesoscopic systems can extract on average heat from their environment when stopped at a cleverly chosen moment and that the second law at stopping times bounds the average extracted heat. Second, we demonstrate that the efficiency at stopping times of an autonomous stochastic heat engine, such as Feymann's ratchet, can be larger than the Carnot efficiency and that the second law of thermodynamics at stopping times bounds its efficiency at stopping times.journal articl
Genomic insights into hybridization of reef corals
No full textHybridization plays a fundamental role in speciation and diversification of plants and animals. Hybridization among highly diverse assemblages of reef corals is well known and widely reported, but the ecological and evolutionary consequences of hybridization among reef corals are only just beginning to become apparent. In this perspective, I introduce introgression and polyploidy in the hybridization (reticulate evolution) of reef corals and then discuss the roles of hybridization in the evolution of Acropora with recent genomic evidence. Finally, I discuss how advances of genomics will facilitate the study of hybridization in reef corals. Together, understanding the genomic basis of reef coral hybridization provides new insights into coral resilience, as well as coral reef biodiversity and conservation.journal articl
Forward genetic screen for Caenorhabditis elegans mutants with a progressive decline in adult locomotor function
Get PDFOkinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophySome inherited mutations can cause a delayed onset of toxic symptoms. These types of mutations can be the underlying cause of age-related diseases or more prevalent agerelated functional impairments. The isolation of mutants and identification of mutations in model organisms that show delayed onset of toxic symptoms may provide insights into evolutionarily conserved genetic regulators that function during the maintenance of functional capacities. In this study, we carried out an unbiased forward genetic screen for Caenorhabditis elegans mutants that show progressive loss of locomotor function during adulthood. After screening 3,352 F2 worms from 1,000 haploid genomes, we isolated five mutant strains that progressively lose their ability to complete a locomotor assay. For one of the mutant strains, a nonsense mutation in Elongator Complex Protein Component 2 (elpc-2) causes the progressive decline in locomotor function. Other C. elegans mutants with mutations in subunits of the Elongator complex also showed progressive declines in adult locomotor function. The Elongator complex may play a critical role during the maintenance of adult locomotor function in C. elegans. The screening procedure, isolated mutants, and the Elongator complex are valuable tools to further explore how locomotor healthspan is maintained in animals.doctoral thesi
Bloodmeal host identification with inferences to feeding habits of a fish-fed mosquito, Aedes baisasi
Get PDFThe mosquito, Aedes baisasi, which inhabits brackish mangrove swamps, is known to feed on fish. However, its host assemblage has not been investigated at the species level. We amplified and sequenced the cytochrome oxidase subunit I barcoding regions as well as some other regions from blood-fed females to identify host assemblages in the natural populations from four islands in the Ryukyu Archipelago. Hosts were identified from 230 females. We identified 15 host fish species belonging to eight families and four orders. Contrary to expectations from previous observations, mudskippers were detected from only 3% of blood-engorged females. The dominant host was a four-eyed sleeper, Bostrychus sinensis (Butidae, Gobiiformes), in Iriomote-jima Island (61%), while it was a snake eel, Pisodonophis boro (Ophichthidae, Anguilliformes), in Amami-oshima and Okinawa-jima islands (78% and 79%, respectively). Most of the identified hosts were known as air-breathing or amphibious fishes that inhabit mangroves or lagoons. Our results suggest that A. baisasi females locate the bloodmeal hosts within the mangrove forests and sometimes in the adjacent lagoons and land on the surface of available amphibious or other air-breathing fishes exposed in the air to feed on their blood.journal articl
Spontaneous emission of a sodium Rydberg atom close to an optical nanofibre
Get PDFWe report on numerical calculations of the spontaneous emission rate of a Rydberg-excited sodium atom in the vicinity of an optical nanofibre. In particular, we study how this rate varies with the distance of the atom to the fibre, the fibre's radius, the symmetry s or p of the Rydberg state as well as its principal quantum number. We find that a fraction of the spontaneously emitted light can be captured and guided along the fibre. This suggests that such a setup could be used for networking atomic ensembles, manipulated in a collective way due to the Rydberg blockade phenomenon.journal articl
Complete Polarization Control for a Nanofiber Waveguide Using Directional Coupling
Get PDFOptical nanofiber waveguides are widely used for near-field delivery and measurement of light. Despite their versatility and efficiency, nanofibers have a critical drawback-their inability to maintain light's polarization state on propagation. Here, we design a directional coupler consisting of two crossed nanofibers to probe the polarization state at the waist region. Directionality of coupling occurs due to asymmetric dipolar emission or spin locking when the evanescent field pattern breaks the mirror symmetry of the crossed-nanofiber system. We demonstrate that, by monitoring the outputs from the directional coupler, two nonorthogonal polarization states can be prepared at the nanofiber waist with a fidelity higher than 99%. Based on these states, we devise a simple and reliable method for complete control of the polarization along a nanofiber waveguide.journal articl
Significant THz absorption in CH3NH2 molecular defect-incorporated organic-inorganic hybrid perovskite thin film
Get PDFThe valid strong THz absorption at 1.58 THz was probed in the organic-inorganic hybrid perovskite thin film, CH3NH3PbI3, fabricated by sequential vacuum evaporation method. In usual solution-based methods such as 2-step solution and antisolvent, we observed the relatively weak two main absorption peaks at 0.95 and 1.87 THz. The measured absorption spectrum is analyzed by density-functional theory calculations. The modes at 0.95 and 1.87 THz are assigned to the Pb-I vibrations of the inorganic components in the tetragonal phase. By contrast, the origin of the 1.58 THz absorption is due to the structural deformation of Pb-I bonding at the grain boundary incorporated with a CH3NH2 molecular defect.journal articl
Long noncoding RNAs in Brassica rapa L. following vernalization
Get PDFBrassica rapa L. is an important agricultural crop that requires a period of prolonged cold for flowering. This process is known as vernalization. Studies have shown that long noncoding RNAs (lncRNAs) play important roles in abiotic stress responses and several cold-responsive noncoding RNAs have been suggested to be involved in vernalization. We examined the transcriptome of the Chinese cabbage inbred line (B. rapa L. var. pekinensis) RJKB-T24, and identified 1,444 long intergenic noncoding RNAs (lincRNAs), 551 natural antisense transcripts (NATs), and 93 intronic noncoding RNAs (incRNAs); 549 of the 2,088 lncRNAs significantly altered their expression in response to four weeks of cold treatment. Most differentially expressed lncRNAs did not lead to a change of expression levels in mRNAs covering or near lncRNAs, suggesting that the transcriptional responses to four weeks of cold treatment in lncRNA and mRNA are independent. However, some differentially expressed mRNAs had NATs with expression altered in the same direction. These genes were categorized as having an abiotic stress response, suggesting that the paired-expression may play a role in the transcriptional response to vernalization or cold treatment. We also identified short-term cold treatment induced NATs in BrFLC and BrMAF genes, which are involved in vernalization. The lncRNAs we identified differed from those reported in Arabidopsis thaliana, suggesting the role of lncRNAs in vernalization differ between these two species.journal articl