• Light based underwater wireless communications

      Oubei, Hassan M.; Shen, Chao; Kammoun, Abla; Zedini, Emna; Park, Kihong; Sun, Xiaobin; Liu, Guangyu; Kang, Chun Hong; Ng, Tien Khee; Alouini, Mohamed-Slim; Ooi, Boon S. (IOP Science, 2018-07-17)
      Underwater wireless optical communication (UWOC) is a wireless communication technology that uses visible light to transmit data in underwater environment. Compared to radio-frequency (RF) and acoustic underwater techniques, UWOC has many advantages including large information bandwidth, unlicensed spectrum and low power requirements. This review paper provides an overview of the latest UWOC research. Additionally, we present a detailed description of transmitter and receiver technologies which are key components of UWOC systems. Moreover, studies investigating underwater optical channel models for both simple attenuation and the impact of turbulence including air bubbles and inhomogeneous salinity and temperature are also described. Future research challenges are identified and outlined.
    • Unleashing the potential of molecular beam epitaxy grown AlGaN-based ultraviolet-spectrum nanowires devices

      Min, Jungwook; Priante, Davide; Tangi, Malleswararao; Liu, Guangyu; Kang, Chun Hong; Prabaswara, Aditya; Zhao, Chao; Al-Maghrabi, Latifah; Alaskar, Yazeed; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S. (SPIE, 2018-07-12)
      There have been recent research advances in AlGaN-based self-assembled nanowires (NWs) as building blocks for ultraviolet (UV) optoelectronics grown by plasma-assisted molecular beam epitaxy. We review the basic growth kinetics on various foundry-compatible-metal/silicon-based substrates and the epistructure design for UV devices. We highlight the use of diffusion-barrier-metal thin film on silicon substrate as a solution to enhance device performance. NWs offer the opportunity to mitigate the detrimental quantum-confined Stark effect (QCSE), which lowers the recombination rate thereby reducing the device efficiency. On the other hand, the polarization-induced doping from the graded composition along NWs can be advantageous for eluding the inefficient doping in AlGaN-based UV devices. Sidewall surface states and the associate passivation treatment, as well as the use of ultrafast electron-microscopy characterization, are crucial investigations in shedding light on device performance under the influence of surface dangling bonds. For investigating the electrical performance of individual NWs and NWs light-emitting diode as a single entity, recent reports based on conductive atomic force microscopy measurements provide fast-prototyping in-process pass-fail evaluation and a means of improving growth for high-performance devices. Stress tests of NWs devices, crucial for reliable operation, are also discussed. Beyond applications in LEDs, an AlGaN-based NWs solar-blind photodetector demonstrated leveraging on the dislocation-free active region, reduced QCSE, enhanced light absorption, and tunable-composition features. The review opens pathways and offers insights for practical realization of AlGaN-based axial NWs devices on scalable and low-cost silicon substrates.
    • Diode junction temperature in ultraviolet AlGaN quantum-disks-in-nanowires

      Priante, Davide; Elafandy, Rami T.; Prabaswara, Aditya; Janjua, Bilal; Zhao, Chao; Alias, Mohd Sharizal; Tangi, Malleswararao; Alaskar, Yazeed; Albadri, Abdulrahman M.; Alyamani, Ahmed Y.; Ng, Tien Khee; Ooi, Boon S. (AIP, 2018-07-05)
      The diode junction temperature (Tj) of light emitting devices is a key parameter affecting the efficiency, output power, and reliability. Herein, we present experimental measurements of the Tj on ultraviolet (UV) AlGaN nanowire (NW) light emitting diodes (LEDs), grown on a thin metal-film and silicon substrate using the diode forward voltage and electroluminescence peak-shift methods. The forward-voltage vs temperature curves show temperature coefficient dVF/dT values of −6.3 mV/°C and −5.2 mV/°C, respectively. The significantly smaller Tj of ∼61 °C is measured for the sample on the metal substrate, as compared to that of the sample on silicon (∼105 °C), at 50 mA, which results from the better electrical-to-optical energy conversion and the absence of the thermally insulating SiNx at the NWs/silicon interface. In contrast to the reported higher Tj values for AlGaN planar LEDs exhibiting low lateral and vertical heat dissipation, we obtained a relatively lower Tj at similar values of injection current. Lower temperatures are also achieved using an Infrared camera, confirming that the Tj reaches higher values than the overall device temperature. Furthermore, the heat source density is simulated and compared to experimental data. This work provides insight into addressing the high junction temperature limitations in light-emitters, by using a highly conductive thin metal substrate, and it aims to realize UV AlGaN NWs for high power and reliable emitting devices.
    • Investigation of Self-injection Locked Visible Laser Diodes for High Bit-rate Visible Light Communication

      Shamim, Md. Hosne Mobarok; Shemis, Mohamed; Shen, Chao; Oubei, Hassan M.; Ng, Tien Khee; Ooi, Boon S.; Khan, Mohammed Zahed Mustafa (IEEE, 2018-06-22)
      We report on self-injection locking in InGaN/GaN (blue/green) and InGaP/AlGaInP (red) visible-light laser diodes. The free-space optical feedback path was accomplished via an external mirror. The effect of injection current, optical power injection ratio, and external cavity length on the spectral linewidth and modulation bandwidth of the lasers are investigated. Our results show that the laser performance was substantially improved. In particular, we achieved a significant increase of ~57% (1.53 GHz - 2.41 GHz) and ~ 31 % (1.72 GHz - 2.26 GHz) in the modulation bandwidth, and ~9 (1.0 nm to 0.11 nm) and ~ 9 (0.63 nm to 0.07nm) times reduction in spectral linewidth of the green and blue lasers, respectively. Consequently, side-mode-suppression-ratio was considerably increased in all the cases, reaching as high as ~20 dB in self-injection locked blue laser diode, thus enabling a close to single mode operation. This work paves the way for attaining high speed optical wireless communications by overcoming the challenges of limited modulation bandwidth and multimode operation of visible laser diodes with this simple scheme.
    • Chick chorioallantoic membrane assay as an in vivo model to study the effect of nanoparticle-based anticancer drugs in ovarian cancer

      Vu, Binh Thanh; Shahin, Sophia Allaf; Croissant, Jonas G.; Fatieiev, Yevhen; Matsumoto, Kotaro; Le-Hoang Doan, Tan; Yik, Tammy; Simargi, Shirleen; Conteras, Altagracia; Ratliff, Laura; Jimenez, Chiara Mauriello; Raehm, Laurence; Khashab, Niveen M.; Durand, Jean-Olivier; Glackin, Carlotta; Tamanoi, Fuyuhiko (Springer Nature, 2018-05-29)
      New therapy development is critically needed for ovarian cancer. We used the chicken egg CAM assay to evaluate efficacy of anticancer drug delivery using recently developed biodegradable PMO (periodic mesoporous organosilica) nanoparticles. Human ovarian cancer cells were transplanted onto the CAM membrane of fertilized eggs, resulting in rapid tumor formation. The tumor closely resembles cancer patient tumor and contains extracellular matrix as well as stromal cells and extensive vasculature. PMO nanoparticles loaded with doxorubicin were injected intravenously into the chicken egg resulting in elimination of the tumor. No significant damage to various organs in the chicken embryo occurred. In contrast, injection of free doxorubicin caused widespread organ damage, even when less amount was administered. The lack of toxic effect of nanoparticle loaded doxorubicin was associated with specific delivery of doxorubicin to the tumor. Furthermore, we observed excellent tumor accumulation of the nanoparticles. Lastly, a tumor could be established in the egg using tumor samples from ovarian cancer patients and that our nanoparticles were effective in eliminating the tumor. These results point to the remarkable efficacy of our nanoparticle based drug delivery system and suggests the value of the chicken egg tumor model for testing novel therapies for ovarian cancer.
    • A finite volume procedure for fluid flow, heat transfer and solid-body stress analysis

      Jagad, P. I.; Puranik, B. P.; Date, A. W. (Informa UK Limited, 2018-04-12)
      A unified cell-centered unstructured mesh finite volume procedure is presented for fluid flow, heat transfer and solid-body stress analysis. An in-house procedure (A. W. Date, Solution of Transport Equations on Unstructured Meshes with Cell-Centered Colocated Variables. Part I: Discretization, International Journal of Heat and Mass Transfer, vol. 48 (6), 1117-1127, 2005) is extended to include the solid-body stress analysis. The transport terms for a cell-face are evaluated in a structured grid-like manner. The Cartesian gradients at the center of each cell-face are evaluated using the coordinate transformation relations. The accuracy of the procedure is demonstrated by solving several benchmark problems involving different boundary conditions, source terms, and types of loading.
    • Strong Exciton–Photon Coupling and Lasing Behavior in All-Inorganic CsPbBr3 Micro/Nanowire Fabry-Pérot Cavity

      Du, Wenna; Zhang, Shuai; Shi, Jia; Chen, Jie; Wu, Zhiyong; Mi, Yang; Liu, Zhixiong; Li, Yuanzheng; Sui, Xinyu; Wang, Rui; Qiu, Xiaohui; Wu, Tao; Xiao, Yunfeng; Zhang, Qing; Liu, Xinfeng (American Chemical Society (ACS), 2018-03-14)
      All-inorganic perovskite micro/nanowire materials hold great promises as nanoscale coherent light source due to their superior optical and electronic properties. The coupling strength between exciton and photon in this system is important for their optical application, however, is rarely studied. In this work, we demonstrated the strong coupling of exciton-photon and polariton lasing in high quality CsPbBr micro/nanowires synthesized by a CVD method. By exploring spatial resolved PL spectra of CsPbBr cavity, we observed mode volume dependent coupling strength with a vacuum Rabi splitting up to 656 meV, as well as significant increase in group index. Moreover, low threshold polariton lasing was achieved at room temperature within strong coupling regime; the polariton characteristic is confirmed by comparing lasing spectra with waveguided output spectra and the dramatically reduced lasing threshold. Our present results provide new avenues to achieve high coupling strengths potentially enabling application of exciting phenomena such as Bose-Einstein condensation of polaritons, efficient light-emitting diodes, and lasers.
    • Species delineation and hybrid identification using diagnostic nuclear markers for Plectropomus leopardus and Plectropomus maculatus

      He, Song; Harrison, Hugo B.; Berumen, Michael L. (Elsevier BV, 2018-06-01)
      Diagnostic molecular markers are an essential tool in the study of species’ ecology and evolution, particularly in closely related and sympatric species. Furthermore, the increasing awareness of wild-hybrids has led to a renewed interest in rapid diagnostic assays. Here, we test the ability of two mitochondrial (Cytb and COI) and two nuclear markers (ETS2 and TMO-4c4) to confidently discriminate purebred P. leopardus and P. maculatus and their first-generation hybrids. A sample of 48 purebred individuals and 91 interspecific hybrids were used in this study and their delineation confirmed using a set of microsatellite markers. Our results indicate mitochondrial markers could not distinguish even between species but both nuclear markers confidently identified species and first-generation hybrids. However, later-generation hybrids could not always be confidently identified due to on-going introgression between species. Our findings provide a robust tool to distinguish purebred individuals and interspecific hybrids in a pair of species with an unexpectedly high incidence of hybridization. The quick species discrimination abilities provided by these diagnostic markers are important for stock assessment and recruitment studies of these important fishery species.
    • Influence of Filler Pore Structure and Polymer on the Performance of MOF-Based Mixed-Matrix Membranes for CO2 Capture

      Sabetghadam, Anahid; Liu, Xinlei; Benzaqui, Marvin; Gkaniatsou, Effrosyni; Orsi, Angelica; Lozinska, Magdalena M.; Sicard, Clemence; Johnson, Timothy; Steunou, Nathalie; Wright, Paul A.; Serre, Christian; Gascon, Jorge; Kapteijn, Freek (Wiley, 2018-03-24)
      To gain insight into the influence of metal-organic framework (MOF) fillers and polymers on membrane performance, eight different composites were studied by combining four MOFs and two polymers. MOF materials (NH-MIL-53(Al), MIL-69(Al), MIL-96(Al) and ZIF-94) with various chemical functionalities, topologies, and dimensionalities of porosity were employed as fillers, and two typical polymers with different permeability-selectivity properties (6FDA-DAM and Pebax) were selected as matrices. The best-performing MOF-polymer composites were prepared by loading 25wt% of MIL-96(Al) as filler, which improved the permeability and selectivity of 6FDA-DAM to 32 and 10%, while for Pebax they were enhanced to 25 and 18%, respectively. The observed differences in membrane performance in the separation of CO from N are explained on the basis of gas solubility, diffusivity properties, and compatibility between the filler and polymer phases.
    • Quantified Hole Concentration in AlGaN Nanowires for High-Performance Ultraviolet Emitters

      Zhao, Chao; Ebaid, Mohamed; Zhang, Huafan; Priante, Davide; Janjua, Bilal; Zhang, Daliang; Wei, Nini; Alhamoud, Abdullah; Shakfa, M. Khaled; Ng, Tien Khee; Ooi, Boon S. (Royal Society of Chemistry (RSC), 2018-05-29)
      P-type doping in wide bandgap and new classes of ultra-wide bandgap materials has long been a scientific and engineering problem. The challenges arise from the large activation energy of dopants and high densities of dislocations in materials. We report here, a significantly enhanced p-type conduction using high-quality AlGaN nanowires. For the first time, the hole concentration in Mg-doped AlGaN nanowires is quantified. The incorporation of Mg into AlGaN was verified by correlation with photoluminescence and Raman measurements. The open-circuit potential measurements further confirmed the p-type conductivity; while Mott-Schottky experiments measured a hole concentration of 1.3×1019 cm-3. These results from photoelectrochemical measurements allow us to design prototype ultraviolet (UV) light-emitting diodes (LEDs) incorporating the AlGaN quantum-disks-in-nanowire and optimized p-type AlGaN contact layer for UV-transparency. The ~335-nm LEDs exhibited a low turn-on voltage of 5 V with a series resistance of 32 Ω, due to the efficient p-type doping of the AlGaN nanowires. The bias-dependent Raman measurements further revealed the negligible self-heating of devices. This study provides an attractive solution to evaluate electrical properties of AlGaN, which is applicable to other wide bandgap nanostructures. Our results are expected to open doors to new applications for wide and ultra-wide bandgap materials.
    • Constructing robust and highly-selective hydrogel membranes by bioadhesion-inspired method for CO 2 separation

      Wu, Yingzhen; Zhou, Tiantian; Wu, Hong; Fu, Weixian; Wang, Xinru; Wang, Shaofei; Yang, Leixin; Wu, Xingyu; Ren, Yanxiong; Jiang, Zhongyi; Wang, Baoyi (Elsevier BV, 2018-06-01)
      Water-swollen hydrogel membranes are good candidates for CO2 separations due to the favorable solubility of CO2 in water. However, the excessive amount of water often causes the poor mechanical property and low selectivity. Herein, we propose a bioadhesion-inspired method to construct robust and high-performance CO2 separation membranes via in situ generation of polydopamine (PDA) nanoaggregates within poly (vinyl alcohol) (PVA) matrix. PDA nanoaggregates entangled with PVA chains and formed hydrogen bonding with hydroxyl groups from PVA chains. Physical cross-linking occurred between PVA chains and PDA nanoaggregates. Compared with the PVA membrane, the PVA-PDA hybrid membrane with the dopamine content of 0.5mol% exhibited a 1.7-fold increase in tensile strength and a 2.2-fold increase in the tensile modulus. The membranes were used for CO2/CH4 separation. The physical cross-linking resulted in a PVA chain rigidification region around PDA nanoaggregates, which hindered the penetration of larger-size gas molecules and thus enhancing the CO2/CH4 selectivity. Moreover, the abundant amine groups from PDA nanoaggregates could facilitate CO2 transport. The optimized hybrid hydrogel membrane exhibited CO2/CH4 selectivity of 43.2, which was 43.85% higher than that of the PVA membrane. The bioadhesion-inspired method opens up new opportunities to exploit the potential application of hydrogel membranes.
    • Carrier dynamics of InxGa1-xN/GaN multiple quantum wells grown on (−201) β-Ga2O3 for bright vertical light emitting diodes

      Mumthaz Muhammed, Mufasila; Xu, Jian; Wehbe, Nimer; Roqan, Iman S. (The Optical Society, 2018-05-30)
      High-quality InxGa1-xN/GaN multi-quantum well (MQW) structures (0.05≤x≤0.13), are successfully grown on transparent and conductive (−201)-oriented β-Ga2O3 substrate. Scanning-transmission electron microscopy and secondary ion mass spectrometry (SIMS) show well-defined high quality MQWs, while the In and Ga compositions in the wells and the barriers are estimated by SIMS. Temperature-dependant Photoluminescence (PL) confirms high optical quality with a strong bandedge emission and negligble yellow band. time-resolved PL measurements (via above/below-GaN bandgap excitations) explain carrier dynamics, showing that the radiative recombination is predominant. Our results demonstrate that (−201)-oriented β-Ga2O3 is a strong candidate as a substrate for III-nitride-based vertical- emitting devices.
    • Flexible InGaN nanowire membranes for enhanced solar water splitting

      Elafandy, Rami T.; Elafandy, Rami T.; Min, Jung-Wook; Zhao, Chao; Ng, Tien Khee; Ooi, Boon S. (The Optical Society, 2018-05-30)
      III-Nitride nanowires (NWs) have recently emerged as potential photoelectrodes for efficient solar hydrogen generation. While InGaN NWs epitaxy over silicon is required for high crystalline quality and economic production, it leads to the formation of the notorious silicon nitride insulating interface as well as low electrical conductivity which both impede excess charge carrier dynamics and overall device performance. We tackle this issue by developing, for the first time, a substrate-free InGaN NWs membrane photoanodes, through liftoff and transfer techniques, where excess charge carriers are efficiently extracted from the InGaN NWs through a proper ohmic contact formed with a high electrical conductivity metal stack membrane. As a result, compared to conventional InGaN NWs on silicon, the fabricated free-standing flexible membranes showed a 10-fold increase in the generated photocurrent as well as a 0.8 V cathodic shift in the onset potential. Through electrochemical impedance spectroscopy, accompanied with TEM-based analysis, we further demonstrated the detailed enhancement within excess charge carrier dynamics of the photoanode membranes. This novel configuration in photoelectrodes demonstrates a novel pathway for enhancing the performance of III-nitrides photoelectrodes to accelerate their commercialization for solar water splitting.
    • The Arabidopsis homolog of human G3BP1 is a key regulator of stomatal and apoplastic immunity

      Abulfaraj, Aala A.; Mariappan, Kiruthiga; Bigeard, Jean; Manickam, Prabhu; Blilou, Ikram; Guo, Xiujie; Al-Babili, Salim; Pflieger, Delphine; Hirt, Heribert; Rayapuram, Naganand (Life Science Alliance, LLC, 2018-05-31)
      Mammalian Ras-GTPase–activating protein SH3-domain–binding proteins (G3BPs) are a highly conserved family of RNA-binding proteins that link kinase receptor-mediated signaling to RNA metabolism. Mammalian G3BP1 is a multifunctional protein that functions in viral immunity. Here, we show that the Arabidopsis thaliana homolog of human G3BP1 negatively regulates plant immunity. Arabidopsis g3bp1 mutants showed enhanced resistance to the virulent bacterial pathogen Pseudomonas syringae pv. tomato. Pathogen resistance was mediated in Atg3bp1 mutants by altered stomatal and apoplastic immunity. Atg3bp1 mutants restricted pathogen entry into stomates showing insensitivity to bacterial coronatine–mediated stomatal reopening. AtG3BP1 was identified as a negative regulator of defense responses, which correlated with moderate up-regulation of salicylic acid biosynthesis and signaling without growth penalty.
    • Towards informed metrics for examining the role of human-induced animal responses in tag studies on wild animals

      Wilson, Rory P.; Holton, Mark; Wilson, Vianney L.; Gunner, Richard; Tysse, Brenda; Wilson, Gwendoline I; Quintana, Flavio; Duarte, Carlos M.; Scantlebury, D. Michael (Wiley, 2018-05-31)
      Two prime issues can detrimentally affect animals that have been equipped with tags; (i) the effect of the capture and restraint process and (ii) the effect of the tag itself. This work examines some of the issues surrounding quantification of tag effects on wild animals for both restrained and free-living animals. A new method to quantify stress effects based on monitoring ventilation rates in relation to activity is suggested for restrained animals which may help improve the practice of handling animals. It is also suggested that various metrics, many derived from accelerometers, can be examined in tagged wild animals to examine the change in behaviours over time with a view to having a better understanding of welfare issues, assuring the quality of recorded data and informing best practice. This article is protected by copyright. All rights reserved.
    • Bacterial polyextremotolerant bioemulsifiers from arid soils improve water retention capacity and humidity uptake in sandy soil

      Raddadi, Noura; Giacomucci, Lucia; Marasco, Ramona; Daffonchio, Daniele; Cherif, Ameur; Fava, Fabio (Springer Nature, 2018-05-31)
      Water stress is a critical issue for plant growth in arid sandy soils. Here, we aimed to select bacteria producing polyextremotolerant surface-active compounds capable of improving water retention and humidity uptake in sandy soils.From Tunisian desert and saline systems, we selected eleven isolates able to highly emulsify different organic solvents. The bioemulsifying activities were stable with 30% NaCl, at 4 and 120 °C and in a pH range 4-12. Applications to a sandy soil of the partially purified surface-active compounds improved soil water retention up to 314.3% compared to untreated soil. Similarly, after 36 h of incubation, the humidity uptake rate of treated sandy soil was up to 607.7% higher than untreated controls.Overall, results revealed that polyextremotolerant bioemulsifiers of bacteria from arid and desert soils represent potential sources to develop new natural soil-wetting agents for improving water retention in arid soils.
    • Candidate enzymes for saffron crocin biosynthesis are localized in multiple cellular compartments

      Demurtas, Olivia Costantina; Frusciante, Sarah; Ferrante, Paola; Diretto, Gianfranco; Azad, Noraddin Hosseinpour; Pietrella, Marco; Aprea, Giuseppe; Taddei, Anna Rita; Romano, Elena; Mi, Jianing; Al-Babili, Salim; Frigerio, Lorenzo; Giuliano, Giovanni (American Society of Plant Biologists (ASPB), 2018-05-29)
      Saffron is composed of the dried stigmas of Crocus sativus and is the most expensive spice on Earth. Its red color is due to the apocarotenoid glycosides, crocins, which accumulate in the vacuole and reach up to 10% of the stigma dry weight. We have previously characterized the first dedicated enzyme in crocin biosynthesis, CsCCD2, which cleaves zeaxanthin to yield crocetin dialdehyde. In this work, we identified six putative aldehyde dehydrogenase (ALDH) transcripts expressed in saffron stigmas. When expressed in E. coli, only one of corresponding proteins (CsALDH3I1), was able to convert crocetin dialdehyde into the crocin precursor, crocetin. CsALDH3I1 carries a C-terminal hydrophobic domain, similar to that of a Neurospora membrane-associated apocarotenoid dehydrogenase, YLO-1. We also characterized a UDP-glycosyltransferase enzyme, CsUGT74AD1, able to convert crocetin to crocins 1 and 2'. In vitro assays showed high specificity of CsALDH3I1 for crocetin dialdehyde and long chain apocarotenals, and of CsUGT74AD1 for crocetin. Upon extract fractionation, the CsCCD2, CsALDH3I1 and CsUGT74AD1 enzymes partitioned in the insoluble fraction, suggesting that they are associated to membranes or to large insoluble complexes. Immunogold labeling of saffron stigmas and confocal microscopy of fusions to Green Fluorescent Protein expressed in N. benthamiana leaves revealed that CsCCD2 localizes to plastids, CsALDH3I1 to the endoplasmic reticulum (ER) and CsUGT74AD1 to the cytoplasm, in association with cytoskeletal-like structures. Based on our and on literature data, we propose that the ER and cytoplasm function as
    • Negative circular polarization emissions from WSe2/MoSe2 commensurate heterobilayers

      Hsu, Wei-Ting; Lu, Li-Syuan; Wu, Po-Hsun; Lee, Ming-Hao; Chen, Peng-Jen; Wu, Pei-Ying; Chou, Yi-Chia; Jeng, Horng-Tay; Li, Lain-Jong; Chu, Ming-Wen; Chang, Wen-Hao (Springer Nature, 2018-04-11)
      Van der Waals heterobilayers of transition metal dichalcogenides with spin-valley coupling of carriers in different layers have emerged as a new platform for exploring spin/valleytronic applications. The interlayer coupling was predicted to exhibit subtle changes with the interlayer atomic registry. Manually stacked heterobilayers, however, are incommensurate with the inevitable interlayer twist and/or lattice mismatch, where the properties associated with atomic registry are difficult to access by optical means. Here, we unveil the distinct polarization properties of valley-specific interlayer excitons using epitaxially grown, commensurate WSe/MoSe heterobilayers with well-defined (AA and AB) atomic registry. We observe circularly polarized photoluminescence from interlayer excitons, but with a helicity opposite to the optical excitation. The negative circular polarization arises from the quantum interference imposed by interlayer atomic registry, giving rise to distinct polarization selection rules for interlayer excitons. Using selective excitation schemes, we demonstrate the optical addressability for interlayer excitons with different valley configurations and polarization helicities.
    • WhiB6 is required for the secretion-dependent regulation of ESX-1 substrates in pathogenic mycobacteria.

      Abdallah, Abdallah; Weerdenburg, Eveline; Guan, Qingtian; Ummels, Roy; Borggreve, S; Adroub, Sabir; Malas, Tareq; Naeem, Raeece; Zhang, Huoming; Otto, Thomas; Bitter, Wilbert; Pain, Arnab (Cold Spring Harbor Laboratory, 2018-04-09)
      The mycobacterial type VII secretion system ESX-1 is responsible for the secretion of a number of proteins that play important roles during host infection. The regulation of the expression of secreted proteins is often essential to establish successful infection. Using transcriptome sequencing, we found that the abrogation of ESX-1 function in Mycobacterium marinum leads to a pronounced increase in gene expression levels of the espA operon during the infection of macrophages, suggesting an important role in ESX-1-mediated virulence during the early phase of infection. In addition, the disruption of ESX-1-mediated protein secretion also leads to a specific down-regulation of the ESX-1 substrates, but not of the structural components of this system, during growth in culture medium. This effect is observed in both M. marinum and M. tuberculosis. We established that down-regulation of ESX-1 substrates is the result of a regulatory process that is influenced by the putative transcriptional regulator whib6, which is located adjacent to the esx-1 locus. In addition, the overexpression of the ESX-1-associated PE35/PPE68 protein pair resulted in a significantly increased secretion of the ESX-1 substrate EsxA, demonstrating a functional link between these proteins. Taken together, these data show that WhiB6 is required for the secretion-dependent regulation of ESX-1 substrates and that ESX-1 substrates are regulated independently from the structural components, both during infection and as a result of active secretion.
    • Accumulation of Carbonates Contributes to Coastal Vegetated Ecosystems Keeping Pace With Sea Level Rise in an Arid Region (Arabian Peninsula)

      Saderne, Vincent; Cusack, Michael; Almahasheer, Hanan; Serrano, Oscar; Masqué, Pere; Arias-Ortiz, Ariane; Krishnakumar, Periyadan Kadinjappalli; Rabaoui, Lotfi; Qurban, Mohammad Ali; Duarte, Carlos M. (American Geophysical Union (AGU), 2018-04-12)
      Anthropogenic sea level rise (SLR) presents one of the greatest risks to human lives and infrastructures. Coastal vegetated ecosystems, that is, tidal marshes, seagrass meadows, and mangrove forests, elevate the seabed through soil accretion, providing a natural coastline protection against SLR. The soil accretion of these ecosystems has never been assessed in hot desert climate regions, where water runoff is negligible. However, tropical marine ecosystems are areas of intense calcification that may constitute an important source of sediment supporting seabed elevation, compensating for the lack of terrestrial inputs. We estimated the long-term (C-centennial) and short-term (Pb-20th century) soil accretion rates (SARs) and inorganic carbon (C) burial in coastal vegetated ecosystems of the Saudi coasts of the central Red Sea and the Arabian Gulf. Short-term SARs (±SE) in mangroves of the Red Sea (0.27 ± 0.22 cm/year) were twofold the SLR for that region since 1925 (0.13 cm/year). In the Arabian Gulf, only mangrove forest SAR is equivalent to local SLR estimates for the period 1979-2007 (0.21 ± 0.09 compared to 0.22 ± 0.05 cm/year, respectively). Long-term SARs are comparable or higher than the global estimates of SLR for the late Holocene (0.01 cm/year). In all habitats of the Red Sea and Arabian Gulf, SARs are supported by high carbonate accretion rates, comprising 40% to 60% of the soil volume. Further studies on the role of carbonates in coastal vegetated ecosystems are required to understand their role in adaptation to SLR.