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The design and control of material interfaces is a foundational approach to realize technologically useful effects and engineer material properties. This is especially true for two-dimensional (2D) materials, where van der Waals stacking allows disparate materials to be freely stacked together to form highly customizable interfaces. This has underpinned a recent wave of discoveries based on excitons in stacked double layers of transition metal dichalcogenides (TMDs), the archetypal family of 2D semiconductors. In such double-layer structures, the elegant interplay of charge, spin and moiré superlattice structure with many-body effects gives rise to diverse excitonic phenomena and correlated physics. Here we review some of the recent discoveries that highlight the versatility of TMD double layers to explore quantum optics and many-body effects. We identify outstanding challenges in the field and present a roadmap for unlocking the full potential of excitonic physics in TMD double layers and beyond, such as incorporating newly discovered ferroelectric and magnetic materials to engineer symmetries and add a new level of control to these remarkable engineered materials. This Review discusses the exciton physics of transition metal dichalcogenides, focusing on moiré patterns and exciton many-body physics, and outlines future research directions in the field., Author(s): Nathan P. Wilson [sup.1] [sup.2] [sup.3] , Wang Yao [sup.4] [sup.5] , Jie Shan [sup.6] , Xiaodong Xu [sup.1] [sup.7] Author Affiliations: (1) Department of Physics, University of Washington, [...]

Author(s): Bevin Huang [1]; Genevieve Clark [2]; Efrn Navarro-Moratalla [3]; Dahlia R. Klein [3]; Ran Cheng [4]; Kyle L. Seyler [1]; Ding Zhong [1]; Emma Schmidgall [1]; Michael A. McGuire [...]

Engineering the electromagnetic environment of a nanometre-scale light emitter by use of a photonic cavity can significantly enhance its spontaneous emission rate, through cavity quantum electrodynamics in the Purcell regime. This effect can greatly reduce the lasing threshold of the emitter (1-5), providing a low-threshold laser system with small footprint, low power consumption and ultrafast modulation. An ultralow-threshold nanoscale laser has been successfully developed by embedding quantum dots into a photonic crystal cavity (PCC) (6-8). However, several challenges impede the practical application of this architecture, including the random positions and compositional fluctuations of the dots (7), extreme difficulty in current injection (8), and lack of compatibility with electronic circuits (7, 8).Here we report a new lasing strategy: an atomically thin crystalline semiconductor--that is, a tungsten diselenide monolayer--is non-destructively and deterministically introduced as a gain medium at the surface of a pre-fabricated PCC. A continuous-wave nanolaser operating in the visible regime is thereby achieved with an optical pumping threshold as low as 27 nanowatts at 130 kelvin, similar to the value achieved in quantum-dot PCC lasers (7). The key to the lasing action lies in the monolayer nature of the gain medium, which confines direct-gap excitons to within one nanometre of the PCC surface. The surface-gain geometry gives unprecedented accessibility and hence the ability to tailor gain properties via external controls such as electrostatic gating and current injection, enabling electrically pumped operation. Our scheme is scalable and compatible with integrated photonics for on-chip optical communication technologies., ] Monolayer transition-met al dichalcogenides (TMDCs) with chemical formula M[X.sub.2] (M = W, Mσ, X = S, Se, Te; see Fig. 1a for the crystal structure) are the first class [...]

The present study investigated the protective effect of L-citrulline on gastric mucosal injury induced by ischemia- reperfusion (IR) in rats. Under anesthesia, the celiac artery was clamped for 30 min, and then the clamp was removed for 60 min reperfusion. Sixty minutes before ischemia, L-citrulline was administered intragastrically at doses of 300, 600, and 900 mg/kg. After the experiment, the stomachs were removed for biochemical and histological examinations. Pretreatment with L-citrulline (300, 600, and 900 mg/kg) significantly ameliorated the gastric damage caused by IR. Moreover, L- citrulline prevented the production of lipid peroxidation and inhibited the increase of myeloperoxidase activity. The elevation in total nitric oxide synthase (NOS) activity, inducible NOS activity, and inducible NOS protein expression as well as the decrease in constitutive NOS activity and gastric mucus level in the gastric mucosa induced by IR were significantly prevented. However, the protective effect mediated by L-citrulline was significantly antagonized by coadministration of L-nitroarginine methyl ester (10 mg/kg, s.c.). These results suggest that part of the mechanism of gastric protection by L-citrulline might be through inhibiting neutrophil infiltration and preserving gastric mucus synthesis and secretion in rats, functions that are closely related to the maintenance of constitutive NOS activity. Key words: L-citrulline, ischemia-reperfusion, nitric oxide, gastric mucus, neutrophil infiltration, rat. La presente etude a eu pour but d'examiner l'effet protecteur de la L-citrulline sur la lesion de la muqueuse gastrique induite par ischemie-reperfusion (IR) chez des rats. Sous anesthesie, on a pose un clamp sur l'artere coeliaque durant 30 min; apres cette periode, on a retire le clamp pour soumettre l'artere a une reperfusion de 60 min. On a administre la L-citrulline par voie intragastrique en doses de 300, 600 et 900 mg/kg, 60 min avant l'ischemie. Apres l'experience, on a preleve les estomacs et effectuer des analyses biochimiques et histologiques. Le pretraitement a la L-citrulline (300, 600 et 900 mg/kg) a significativement diminue la lesion gastrique causee par IR. De plus, la L-citrulline a prevenu la peroxydation des lipides et l'augmentation de l'activite de la myeloperoxydase. Elle a aussi empeche de facon significative l'elevation de l'activite totale de la NO synthase (NOS), de l'activite de la NOS inductible et de l'expression de la proteine NOS inductible, ainsi que la diminution du taux de mucus et de l' activite de la NOS constitutive dans la muqueuse gastrique. Toutefois, la coadministration de L-nitroarginine ester methylique (10 mg/kg, s.c.) a antagonise de maniere considerable l'effet protecteur vehicule par la L-citrulline. Ces resultats donnent a penser que le mecanisme de protection gastrique par la L-citrulline pourrait impliquer l' inhibition de l' infiltration des neutrophiles et la preservation de la synthese et de la secretion de la muqueuse gastrique, qui sont etroitement associees au maintien de l'activite de constitutive NOS. Mots-cles : L-citrulline, ischemie-reperfusion, monoxyde d'azote, mucus gastrique, infiltration des neutrophiles, rat. [Traduit par la Redaction], Introduction Gastric ischemia-reperfusion (IR) injury is a significant problem in numerous situations such as trauma, major surgery, and nonsteroidal anti-inflammatory drug administration (Kitahora and Guth 1987; Villegas et al. 2004). [...]

Extraordinary variation has been found in mitochondrial (mt) genome inheritance, gene content and arrangement among bivalves. However, only few bivalve mt genomes have been comparatively analyzed to infer their evolutionary scenarios. In this study, the complete mt genome of the venerid Paphia euglypta (Bivalvia: Veneridae) was firstly studied and, secondly, it was comparatively analyzed with other venerids (e.g., Venerupis philippinarum and Meretrix petechialis) to better understand the mt genome evolution within a family. Though several common features such as the AT content, codon usage of protein-coding genes, and AT/GC skew are shared by the three venerids, a high level of variability is observed in genome size, gene content, gene order, arrangements and primary sequence of nucleotides or amino acids. Most of the gene rearrangement can be explained by the 'tandem duplication and random loss' model. From the observed rearrangement patterns, we speculate that block interchange between adjacent genes may be common in the evolution of mt genomes in venerids. Furthermore, this study presents several new findings in mt genome annotation of V. philippinarum and M. petechialis, and hence we have reannotated the genome of these two species as: (1) the ORF of the formerly annotated cox2 gene in V. philippinarum is deduced by using a truncated 'T' codon and a second cox2 gene is identified; (2) the trnS-AGN gene is identified and marked in the mt genome of both venerids. Thus, this study demonstrated a high variability of mt genomes in the Veneridae, and showed the importance of comparative mt genome analysis to interpret the evolution of the bivalve mt genome. Key words: Paphia euglypta, mitochondrial genome, comparative analysis, Veneridae, gene arrangement. Une variation extraordinaire a ete observeee en ce qui a trait a la transmission, au contenu genique et a l'arrangement du genome mitochondrial (mt) chez les bivalves. Cependant, seuls quelques genomes mt ont ete; compares chez les bivalves pour en comprendre revolution. Dans ce travail, le genome mt complet du Veneride Paphia euglypta (Bivalvia : Veneridae) a ete etudiee et ensuite compare a ceux d'autres Venerides (e.g., Venerupis philippinarum et Meretrix petechialis) afin de mieux comprendre revolution du genome mt au sein d'une famille. Bien que plusieurs caracteiristiques etaient semblables chez les trois Veneeridees, comme le contenu en AT, l'usage des codons au sein des regions codant pour des proteines et le biais AT/GC, une grande variabilite aete observeee en ce qui a trait a la taille du genome, le contenu et l'ordre genique, l'arrangement et la sequence primaire des nucleotides ou des acides amines. La plupart des rearrangements geniques pouvaient s'expliquer via le modele de << duplication en tandem suivie d'une perte aleeatoire >>. A partir des rearrangements observeis, les auteurs proposent que l'echange de blocs entre genes adjacents pourrait etre un phenome:ne repandu dans revolution des genomes mt chez les Vererides. De plus, cette etude presente plusieurs nouvelles trouvailles en matiere d'annotation des genomes mt chez le V. philippinarum et le M. petechialis. Les auteurs ont ainsi produit une nouvelle annotation du genome mt de ces deux especes avec les modifications suivantes : 1) l'ORF du gene precedemment annote comme etant cox2 chez le V. philippinarum aeetee deeduit en utilisant un codon << T >> tronquee et un second geene cox2 aete identified ;2)etlegene trnS-AGN aetee identifiee et annotee dans les genomes mt des deux especes. Ainsi, cette etude a montre la grande variabilitee des genomes mt chez les Venerides et l'importance de l'analyse compareee des genomes mt pour deduire revolution du geenome mt chez les bivalves. Mots-cles : Paphia euglypta,genome mitochondrial, analyse compareee, Venerides, arrangement geenique., Introduction Complete mitochondrial (mt) genomes have been widely used in metazoan phylogenetic analyses and genome evolution studies because of their high content of information, maternal inheritance, and low frequency of [...]

A single electron or hole spin trapped inside a semiconductor quantum dot forms the foundation for many proposed quantum logic devices (1-6). In group III-V materials, the resonance and coherence between two ground states of the single spin are inevitably affected by the lattice nuclear spins through the hyperfine interaction (7-9), while the dynamics of the single spin also influence the nuclear environment (10-15). Recent efforts (12,16) have been made to protect the coherence of spins in quantum dots by suppressing the nuclear spin fluctuations. However, coherent control of a single spin in a single dot with simultaneous suppression of the nuclear fluctuations has yet to be achieved. Here we report the suppression of nuclear field fluctuations in a singly charged quantum dot to well below the thermal value, as shown by an enhancement of the single electron spin dephasing time [T.sub.2] *, which we measure using coherent dark-state spectroscopy. The suppression of nuclear fluctuations is found to result from a hole-spin assisted dynamic nuclear spin polarization feedback process, where the stable value of the nuclear field is determined only by the laser frequencies at fixed laser powers. This nuclear field locking is further demonstrated in a three-laser measurement, indicating a possible enhancement of the electron spin [T.sub.2] * by a factor of several hundred. This is a simple and powerful method of enhancing the electron spin coherence time without use of 'spin echo'-type techniques (8,12). We expect that our results will enable the reproducible preparation of the nuclear spin environment for repetitive control and measurement of a single spin with minimal statistical broadening., We performed the experiment on a single negatively charged quantum dot embedded in a Schottky diode structure. Figure 1a shows the four-level energy diagram of the trion states under an [...]

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion ([Pb.sup.2+]) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to [Pb.sup.2+]and the use of DNA--Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for [Pb.sup.2+] is immobilized onto an Au electrode surface via a thiol--Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA--Au biobar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru[(N[H.sub.3]).sub.6.sup.3+], which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of [Pb.sup.2+] to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru[(N[H.sub.3]).sub.6.sup.3+] from the Au electrode surface. The release of Ru[(N[H.sub.3]).sub.6.sup.3+] results in lower electrochemical signal of Ru[(N[H.sub.3]).sub.6.sup.3+] confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru[(N[H.sub.3]).sub.6.sup.3+] provides quantitative measures of the concentrations of [Pb.sup.2+], with a linear calibration ranging from 5 nM to 0.1 [micro]M. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru[(N[H.sub.3]).sub.6.sup.3+], the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of [Pb.sup.2+] at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for [Pb.sup.2+]. Although this DNAzyme sensor is demonstrated for the detection of [Pb.sup.2+], it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.

While firm growth critically depends on financing ability and access to external capital, the operations management and engineering economics literature seldom considers the effects of financial constraints on the firms' operational decisions. Another critical assumption in traditional operations models is that corporate managers always act in the firm owners' best interests. Managers are, however, agents of the owners of the company, whose interests are often not aligned with those of equity holders or debt holders; hence, managers may make major decisions that are suboptimal from the firm owners' point of view. This article builds on a news vendor model to make optimal production decisions in the presence of financial constraints and managerial incentives. We explore the relationship between operating conditions and financial leverage and observe that financial leverage can increase as margins reach either low or high extremes. We also provide some empirical support for this observation. We further extend our model to consider the effects of agency costs on the firm's production decision and debt choice by including performance-based bonuses in the manager's compensation. Our analyses show how managerial incentives may drive a manager to deviate from firm-optimal decisions and that low-margin producers face significant risk from this agency cost while high-margin producers face relatively low risk in using such compensation., INTRODUCTION The operations management and engineering economics literature has largely ignored corporate financing decisions on the assumption that a firm's optimal inventory level or production decisions can be fully financed [...]

Understanding how nutrients affect gene expression will help us to understand the mechanisms controlling plant growth and development as a function of nutrient availability. Nitrate has been shown to serve as a signal for the control of gene expression in Arabidopsis. There is also evidence, on a gene-by-gene basis, that downstream products of nitrogen (N) assimilation such as glutamate (Glu) or glutamine (Gin) might serve as signals of organic N status that in turn regulate gene expression. To identify genome-wide responses to such organic N signals, Arabidopsis seedlings were transiently treated with ammonium nitrate in the presence or absence of MSX, an inhibitor of glutamine synthetase, resulting in a block of Glu/GIn synthesis. Genes that responded to organic N were identified as those whose response to ammonium nitrate treatment was blocked in the presence of MSX. We showed that some genes previously identified to be regulated by nitrate are under the control of an organic N-metabolite. Using an integrated network model of molecular interactions, we uncovered a subnetwork regulated by organic N that included CCA1 and target genes involved in N-assimilation. We validated some of the predicted interactions and showed that regulation of the master clock control gene CCA1 by Glu or a Glu-derived metabolite in turn regulates the expression of key N-assimilatory genes. Phase response curve analysis shows that distinct N-metabolites can advance or delay the CCA1 phase. Regulation of CCA 1 by organic N signals may represent a novel input mechanism for N-nutrients to affect plant circadian clock function. circadian | gene networks | glutamate | metabolism

FRET is a well established method for cellular and subcellular imaging of protein interactions. However, FRET obligatorily necessitates fluorescence excitation with its concomitant problems of photobleaching, autofluorescence, phototoxicity, and undesirable stimulation of photobiological processes. A sister technique, bioluminescence resonance energy transfer (BRET), avoids these problems because it uses enzyme-catalyzed luminescence; however, BRET signals usually have been too dim to image effectively in the past. Using a new generation electron bombardment-charge-coupled device camera coupled to an image splitter, we demonstrate that BRET can be used to image protein interactions in plant and animal cells and in tissues; even subcellular imaging is possible. We have applied this technology to image two different protein interactions: (i) dimerization of the developmental regulator, COP1, in plant seedlings; and (ii) CCAAT/ enhancer binding protein [alpha] (C/EBP[alpha]) in the mammalian nucleus. This advance heralds a host of applications for imaging without fluorescent excitation and its consequent limitations. C/EBP | COP1 | FRET | luminescence | fluorescence

Bioluminescence resonance energy transfer (BRET) between Renilla luciferase and yellow fluorescent protein has been adapted to serve as a real-time reporter on protein-protein interactions in live plant cells by using the Arabidopsis Constitutive photomorphogenesis 1 (COP1) protein as a model system. COP1 is a repressor of light signal transduction that functions as part of a nuclear E3 ubiquitin ligase. COP1 possesses a leucine-rich nuclear-exclusion signal that resides in a domain implicated in COP1 dimerization. BRET was applied in conjunction with site-directed mutagenesis to explore the respective contributions of the nuclear-exclusion and dimerization motifs to the regulation of COP1 activity in vivo. One specific mutant protein, [COP1.sup.L105A], showed increased nuclear accumulation but retained the ability to dimerize, as monitored by BRET, whereas other mutations inhibited both nuclear exclusion and COP1 dimerization. Mutant rescue and overexpression experiments indicated that nuclear exclusion of COP1 protein is a rate-limiting step in light signal transduction. dimerization | photomorphogenesis | nuclear export

Host-guest chemistry is relevant to the development of microsensors to monitor pollutants. Coordination and host-guest chemistry is used in designing electrochemical sensors geared to detecting ammonium and alkali metal ions. Coordination complexes are used for the sensor molecules, and involve a functionalized tripodal ligand and a copper ion. Copper complexes function as efficient redox-active receptors since the electrochemical behavior shown when binding occurs with a guest is well-defined.