153 research outputs found
Direct Nano-Imaging of Light-Matter Interactions in Nanoscale Excitonic Emitters
Strong light-matter interactions in localized nano-emitters when placed near
metallic mirrors have been widely reported via spectroscopic studies in the
optical far-field. Here, we report a near-field nano-spectroscopic study of the
localized nanoscale emitters on a flat Au substrate. We observe strong-coupling
of the excitonic dipoles in quasi 2-dimensional CdSe/CdxZnS1-xS nanoplatelets
with gap mode plasmons formed between the Au tip and substrate. We also observe
directional propagation on the Au substrate of surface plasmon polaritons
launched from the excitons of the nanoplatelets as wave-like fringe patterns in
the near-field photoluminescence maps. These fringe patterns were confirmed via
extensive electromagnetic wave simulations to be standing-waves formed between
the tip and the emitter on the substrate plane. We further report that both
light confinement and the in-plane emission can be engineered by tuning the
surrounding dielectric environment of the nanoplatelets. Our results lead to
renewed understanding of in-plane, near-field electromagnetic signal
transduction from the localized nano-emitters with profound implications in
nano and quantum photonics as well as resonant optoelectronics.Comment: manuscript + supporting informatio
Ultrastrong Light-Matter Coupling in 2D Metal-Chalcogenates
Hybridization of excitons with photons to form hybrid quasiparticles,
exciton-polaritons (EPs), has been widely investigated in a range of
semiconductor material systems coupled to photonic cavities. Self-hybridization
occurs when the semiconductor itself can serve as the photonic cavity medium
resulting in strongly-coupled EPs with Rabi splitting energies > 200 meV at
room temperatures which recently were observed in layered two-dimensional (2D)
excitonic materials. Here, we report an extreme version of this phenomenon, an
ultrastrong EP coupling, in a nascent, 2D excitonic system, the metal organic
chalcogenate (MOCHA) compound named mithrene. The resulting self-hybridized EPs
in mithrene crystals placed on Au substrates show Rabi Splitting in the
ultrastrong coupling range (> 600 meV) due to the strong oscillator strength of
the excitons concurrent with the large refractive indices of mithrene. We
further show bright EP emission at room temperature as well as EP dispersions
at low-temperatures. Importantly, we find lower EP emission linewidth narrowing
to ~1 nm when mithrene crystals are placed in closed Fabry-Perot cavities. Our
results suggest that MOCHA materials are ideal for polaritonics in the deep
green-blue part of the spectrum where strong excitonic materials with large
optical constants are notably scarce
Programming moir\'e patterns in 2D materials by bending
Moir\'e superlattices in twisted two-dimensional materials have generated
tremendous excitement as a platform for achieving quantum properties on demand.
However, the moir\'e pattern is highly sensitive to the interlayer atomic
registry, and current assembly techniques suffer from imprecise control of the
average twist angle, spatial inhomogeneity in the local twist angle, and
distortions due to random strain. Here, we demonstrate a new way to manipulate
the moir\'e patterns in hetero- and homo-bilayers through in-plane bending of
monolayer ribbons, using the tip of an atomic force microscope. This technique
achieves continuous variation of twist angles with improved twist-angle
homogeneity and reduced random strain, resulting in moir\'e patterns with
highly tunable wavelength and ultra-low disorder. Our results pave the way for
detailed studies of ultra-low disorder moir\'e systems and the realization of
precise strain-engineered devices
C/EBPβ Promotes Transition from Proliferation to Hypertrophic Differentiation of Chondrocytes through Transactivation of p57Kip2
BACKGROUND: Although transition from proliferation to hypertrophic differentiation of chondrocytes is a crucial step for endochondral ossification in physiological skeletal growth and pathological disorders like osteoarthritis, the underlying mechanism remains an enigma. This study investigated the role of the transcription factor CCAAT/enhancer-binding protein beta (C/EBPbeta) in chondrocytes during endochondral ossification. METHODOLOGY/PRINCIPAL FINDINGS: Mouse embryos with homozygous deficiency in C/EBPbeta (C/EBPbeta-/-) exhibited dwarfism with elongated proliferative zone and delayed chondrocyte hypertrophy in the growth plate cartilage. In the cultures of primary C/EBPbeta-/- chondrocytes, cell proliferation was enhanced while hypertrophic differentiation was suppressed. Contrarily, retroviral overexpression of C/EBPbeta in chondrocytes suppressed the proliferation and enhanced the hypertrophy, suggesting the cell cycle arrest by C/EBPbeta. In fact, a DNA cell cycle histogram revealed that the C/EBPbeta overexpression caused accumulation of cells in the G0/G1 fraction. Among cell cycle factors, microarray and real-time RT-PCR analyses have identified the cyclin-dependent kinase inhibitor p57(Kip2) as the transcriptional target of C/EBPbeta. p57(Kip2) was co-localized with C/EBPbeta in late proliferative and pre-hypertrophic chondrocytes of the mouse growth plate, which was decreased by the C/EBPbeta deficiency. Luciferase-reporter and electrophoretic mobility shift assays identified the core responsive element of C/EBPbeta in the p57(Kip2) promoter between -150 and -130 bp region containing a putative C/EBP motif. The knockdown of p57(Kip2) by the siRNA inhibited the C/EBPbeta-induced chondrocyte hypertrophy. Finally, when we created the experimental osteoarthritis model by inducing instability in the knee joints of adult mice of wild-type and C/EBPbeta+/- littermates, the C/EBPbeta insufficiency caused resistance to joint cartilage destruction. CONCLUSIONS/SIGNIFICANCE: C/EBPbeta transactivates p57(Kip2) to promote transition from proliferation to hypertrophic differentiation of chondrocytes during endochondral ossification, suggesting that the C/EBPbeta-p57(Kip2) signal would be a therapeutic target of skeletal disorders like growth retardation and osteoarthritis
Drosophila Genome-Wide RNAi Screen Identifies Multiple Regulators of HIF–Dependent Transcription in Hypoxia
Hypoxia-inducible factors (HIFs) are a family of evolutionary conserved alpha-beta heterodimeric transcription factors that induce a wide range of genes in response to low oxygen tension. Molecular mechanisms that mediate oxygen-dependent HIF regulation operate at the level of the alpha subunit, controlling protein stability, subcellular localization, and transcriptional coactivator recruitment. We have conducted an unbiased genome-wide RNA interference (RNAi) screen in Drosophila cells aimed to the identification of genes required for HIF activity. After 3 rounds of selection, 30 genes emerged as critical HIF regulators in hypoxia, most of which had not been previously associated with HIF biology. The list of genes includes components of chromatin remodeling complexes, transcription elongation factors, and translational regulators. One remarkable hit was the argonaute 1 (ago1) gene, a central element of the microRNA (miRNA) translational silencing machinery. Further studies confirmed the physiological role of the miRNA machinery in HIF–dependent transcription. This study reveals the occurrence of novel mechanisms of HIF regulation, which might contribute to developing novel strategies for therapeutic intervention of HIF–related pathologies, including heart attack, cancer, and stroke
A Symmetric Dual Feedback System Provides a Robust and Entrainable Oscillator
Many organisms have evolved molecular clocks to anticipate daily changes in their environment. The molecular mechanisms by which the circadian clock network produces sustained cycles have extensively been studied and transcriptional-translational feedback loops are common structures to many organisms. Although a simple or single feedback loop is sufficient for sustained oscillations, circadian clocks implement multiple, complicated feedback loops. In general, different types of feedback loops are suggested to affect the robustness and entrainment of circadian rhythms
Prediction of Cellular Burden with Host--Circuit Models
Heterologous gene expression draws resources from host cells. These resources
include vital components to sustain growth and replication, and the resulting
cellular burden is a widely recognised bottleneck in the design of robust
circuits. In this tutorial we discuss the use of computational models that
integrate gene circuits and the physiology of host cells. Through various use
cases, we illustrate the power of host-circuit models to predict the impact of
design parameters on both burden and circuit functionality. Our approach relies
on a new generation of computational models for microbial growth that can
flexibly accommodate resource bottlenecks encountered in gene circuit design.
Adoption of this modelling paradigm can facilitate fast and robust design
cycles in synthetic biology
Species-Area Relationships Are Controlled by Species Traits
The species-area relationship (SAR) is one of the most thoroughly investigated empirical relationships in ecology. Two theories have been proposed to explain SARs: classical island biogeography theory and niche theory. Classical island biogeography theory considers the processes of persistence, extinction, and colonization, whereas niche theory focuses on species requirements, such as habitat and resource use. Recent studies have called for the unification of these two theories to better explain the underlying mechanisms that generates SARs. In this context, species traits that can be related to each theory seem promising. Here we analyzed the SARs of butterfly and moth assemblages on islands differing in size and isolation. We tested whether species traits modify the SAR and the response to isolation. In addition to the expected overall effects on the area, traits related to each of the two theories increased the model fit, from 69% up to 90%. Steeper slopes have been shown to have a particularly higher sensitivity to area, which was indicated by species with restricted range (slope = 0.82), narrow dietary niche (slope = 0.59), low abundance (slope = 0.52), and low reproductive potential (slope = 0.51). We concluded that considering species traits by analyzing SARs yields considerable potential for unifying island biogeography theory and niche theory, and that the systematic and predictable effects observed when considering traits can help to guide conservation and management actions
No Weight for “Due Weight”? A Children’s Autonomy Principle in Best Interest Proceedings
Article 12 of the un Convention on the Rights of the Child (crc) stipulates that children should have their views accorded due weight in accordance with age and maturity, including in proceedings affecting them. Yet there is no accepted understanding as to how to weigh children’s views, and it is associated strongly with the indeterminate notion of “competence”. In this article, case law and empirical research is drawn upon to argue that the concept of weighing their views has been an obstacle to children’s rights, preventing influence on outcomes for children in proceedings in which their best interests are determined. Younger children and those whose wishes incline against the prevailing orthodoxy (they may resist contact with a parent, for example) particularly lose out. Children’s views appear only to be given “significant weight” if the judge agrees with them anyway. As it is the notion of autonomy which is prioritised in areas such as medical and disability law and parents’ rights, it is proposed in this article that a children’s autonomy principle is adopted in proceedings – in legal decisions in which the best interest of the child is the primary consideration, children should get to choose, if they wish, how they are involved and the outcome, unless it is likely that significant harm will arise from their wishes. They should also have “autonomy support” to assist them in proceedings. This would likely ensure greater influence for children and require more transparent decision-making by adults.</jats:p
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