• Reduced ion migration and enhanced photoresponse in cuboid crystals of methylammonium lead iodide perovskite

      Zhumekenov, Ayan A; Haque, Mohammed; Yin, Jun; El-Zohry, Ahmed M.; Lee, Kwang Jae; Dursun, Ibrahim; Mohammed, Omar F.; Baran, Derya; Bakr, Osman (IOP Publishing, 2018-11-10)
      The optoelectronic and photocatalytic properties of a number of semiconductor materials, including halide perovskites, have recently been found to be facet-dependent. While methylammonium lead iodide (CH3NH3PbI3) perovskite – an important material for energy applications – has shown facet-dependent electronic properties as well, most studies on CH3NH3PbI3 perovskite were performed on rhombo-dodecahedral (or rhombic) single crystals with the (200) and (112) facets exposed. In contrast, less is known about the electronic properties, including mixed conductivity behavior and possible in-plane anisotropy, of the (002) facet. Thus, we report a facile method for the growth of cuboid crystals of CH3NH3PbI3 perovskite with the (002) and (110) facets exposed. Two-terminal devices fabricated on the (002) facet demonstrate significantly improved charge transport and optoelectronic characteristics compared to those on the (200) facet of typical rhombic crystals, including: reduced ion migration, low dark current, and temporally-stable high photocurrents. These desirable characteristics of cuboid crystals are linked to their favorable growth conditions and preferred facet orientations. Our results provide a guidance for utilizing facets and crystal growth to achieve more efficient in-plane halide perovskite devices.
    • Theileria\n highjacks JNK2 into a complex with the macroschizont GPI-anchored surface protein p104

      de Laté, Perle Latré; Haidar, Malak; Ansari, Hifzur Rahman; Tajeri, Shahin; Szarka, Eszter; Alexa, Anita; Woods, Kerry; Reményi, Attila; Pain, Arnab; Langsley, Gordon (Wiley, 2018-11-09)
      Constitutive JNK activity characterizes bovine T and B cells infected with Theileria parva, and B cells and macrophages infected with T. annulata. Here, we show that T. annulata infection of macrophages manipulates JNK activation by recruiting JNK2 and not JNK1 to the parasite surface, whereas JNK1 is found predominantly in the host cell nucleus. At the parasite's surface JNK2 forms a complex with p104 a GPI-anchored T. annulata plasma membrane protein. Sequestration of JNK2 depended on PKA-mediated phosphorylation of a JNK-binding motif common to T. parva and a cell penetrating peptide harbouring the conserved p104 JNK-binding motif competitively ablated binding, whereupon liberated JNK2 became ubiquitinated and degraded. Cytosolic sequestration of JNK2 suppressed small mitochondrial ARF-mediated autophagy, whereas it sustained nuclear JNK1 levels, c-Jun phosphorylation and matrigel traversal. Therefore, T. annulata sequestration of JNK2 contributes to both survival and dissemination of Theileria-transformed macrophages.
    • OPA2Vec: combining formal and informal content of biomedical ontologies to improve similarity-based prediction

      Smaili, Fatima Z.; Gao, Xin; Hoehndorf, Robert (Oxford University Press (OUP), 2018-11-07)
      Motivation:Ontologies are widely used in biology for data annotation, integration, and analysis. In addition to formally structured axioms, ontologies contain meta-data in the form of annotation axioms which provide valuable pieces of information that characterize ontology classes. Annotation axioms commonly used in ontologies include class labels, descriptions, or synonyms. Despite being a rich source of semantic information, the ontology meta-data are generally unexploited by ontology-based analysis methods such. Results:We propose a novel method, OPA2Vec, to generate vector representations of biological entities in ontologies by combining formal ontology axioms and annotation axioms from the ontology metadata. We apply a Word2Vec model that has been pre-trained on either a corpus or abstracts or full-text articles to produce feature vectors from our collected data. We validate our method in two different ways: first, we use the obtained vector representations of proteins in a similarity measure to predict protein-protein interaction on two different datasets. Second, we evaluate our method on predicting gene-disease associations based on phenotype similarity by generating vector representations of genes and diseases using a phenotype ontology, and applying the obtained vectors to predict gene-disease associations using mouse model phenotypes. We demonstrate that OPA2Vec significantly outperforms existing methods for predicting gene-disease associations. Using evidence from mouse models, we apply OPA2Vec to identify candidate genes for several thousand rare and orphan diseases. OPA2Vec can be used to produce vector representations of any biomedical entity given any type of biomedical ontology. Availability:https://github.com/bio-ontology-research-group/opa2vec.
    • Lexicographic Codebook Design for OFDM with Index Modulation

      Dang, Shuping; Chen, Gaojie; Coon, Justin P. (Institute of Electrical and Electronics Engineers (IEEE), 2018-11-06)
      In this paper, we propose a novel codebook design scheme for orthogonal frequency-division multiplexing with index modulation (OFDM-IM) to improve system performance. The optimization process can be implemented efficiently by the lexicographic ordering principle. By applying the proposed codebook design, all subcarrier activation patterns with a fixed number of active subcarriers will be explored. Furthermore, as the number of active subcarriers is fixed, the computational complexity for estimation at the receiver is reduced and the zero-active subcarrier dilemma is solved without involving complex higher layer transmission protocols. It is found that the codebook design can potentially provide a trade-off between diversity and transmission rate. We investigate the diversity mechanism and formulate three diversity-rate optimization problems for the proposed OFDMIM system. Based on the genetic algorithm (GA), the method of solving these formulated optimization problems is provided and verified to be effective. Then, we analyze the average block error rate (BLER) and bit error rate (BER) of OFDM-IM systems applying the codebook design. Finally, all analyses are numerically verified by Monte Carlo simulations. In addition, a series of comparisons are provided, by which the superiority of the codebook design is thereby confirmed.
    • A minimal hyperbolic system for unstable shock waves

      Kabanov, Dmitry I.; Kasimov, Aslan R. (Elsevier, 2018-11-06)
      We present a computational analysis of a 2×2 hyperbolic system of balance laws whose solutions exhibit complex nonlinear behavior. Traveling-wave solutions of the system are shown to undergo a series of bifurcations as a parameter in the model is varied. Linear and nonlinear stability properties of the traveling waves are computed numerically using accurate shock-fitting methods. The model may be considered as a minimal hyperbolic system with chaotic solutions and can also serve as a stringent numerical test problem for systems of hyperbolic balance laws.
    • Regulation of Ni-CNT Interaction on Mn Promoted Nickel Nanocatalysts Supported on Oxygenated CNTs for CO2 Selective Hydrogenation

      Li, Jing; Zhou, Yanan; Xiao, Xin; Wang, Wei; Wang, Ning; Qian, Weizhong; Chu, Wei (American Chemical Society (ACS), 2018-11-06)
      Mn promoted Ni nanoparticles (NPs) supported on oxygen-functionalized carbon nanotubes (CNTs) was synthesized for CO2 hydrogenation to methane. This novel metal-carbon catalytic system was characterized by both experimental and computational studies. An anomalous metal-support interaction mode (i.e. a higher temperature would lead to a weakened Ni-CNT interaction) was observed. Deep investigation confirmed that surface oxygen groups (SOGs) on CNTs played a key role in tuning the Ni-CNT interaction. We proposed that high calcination temperature would firstly lead to the decomposition of SOGs (> 400 oC), then causing a loss of anchoring sites and the anchoring effect of SOGs on Ni NPs, thus cutting off the connection between interfacial Ni atoms and CNT body, so resulting in the migration and coalescence of fine flat Ni NPs into larger sphere ones at 550 oC (geometric effect). Density functional calculation (DFT) study clarified this kind of anchoring effect stemmed from the formation of covalent bonding between interfacial Ni atom and C or O elements of SOGs, causing electrons transferred from Ni atoms to CNT support because of the intrinsic electronegativity of -COOH (electronic effect). Besides, Mn promotion notably boost the activity compared with unpromoted catalysts, which was irrelevant with the size effect but the enhanced CO2 adsorption and conversion according to the result of CO2-TPD and transient response experiment. The optimized NiMn350 catalyst endowed with Mn promotion and robust Ni-CNT interaction, showed both high activity and sintering resistance more than 140-hour. Our findings paved the way to reasonably design the metal-carbon catalyst with both high activity and stability.
    • Creation of a thermally assisted skyrmion lattice in Pt/Co/Ta multilayer films

      Zhang, Senfu; Zhang, Junwei; Wen, Yan; Chudnovsky, Eugene M.; Zhang, Xixiang (AIP Publishing, 2018-11-06)
      Néel-type magnetic skyrmions in multilayer films have recently attracted significant attention due to their stability at room temperature and low threshold for current-driven motion, offering the potential for the construction of high-speed and high-density spintronic devices. However, to date, research studies reported in the literature have rarely examined the effect of temperature on the formation and behavior of Néel-type skyrmions. Here, we investigate the effect of the temperature on the creation of a skyrmion lattice in [Pt/Co/Ta]10 multilayer samples, using in-situ Lorentz transmission electron microscopy. By imaging the magnetization reversal process from a positive (negative) to a negative (positive) saturation, we find that the skyrmions can be created by nucleation from a ferromagnetic state and by breaking the labyrinth domains under certain external fields. More importantly, we demonstrate that the density of skyrmions in the multilayers not only depend on the external magnetic field, but also depend on the temperature and the thermal history of the materials.
    • Analysis of Climate Trends and Leading Modes of Climate Variability for MENA Region

      Dogar, Muhammad Mubashar; Sato, Tomonori (American Geophysical Union (AGU), 2018-11-05)
      The Middle East and North Africa (MENA), primarily the Arabian Peninsula (AP) is a region where the rate of mean surface temperature rise per decade is among the highest globally known during the recent past. Moreover, MENA regional climate is very sensitive to internal and external climate drivers. Therefore, it is of significant practical importance to analyze MENA sensitivity to climate trends as well as leading variability modes such as El Nino Southern Oscillation (ENSO), North Atlantic Oscillation (NAO) and Indian summer monsoon (ISM). Using multiple regression technique on observations and the high-resolution atmospheric model (HiRAM) output, this study investigates the role of climate trends, and leading circulation modes such as NAO, ENSO, and ISM in inducing temperature and precipitation variability in MENA region for the period 1979-2008. Our results show substantial regional temperature and precipitation responses of ENSO, NAO, and ISM over MENA. Both the model and the observations indicate that positive phase of NAO and ENSO significantly cools central parts of MENA, in particular, the AP in winter. However, in boreal summer, the warm ENSO phase produces significant warming and drying over the tropical region. The strengthening (weakening) of ISM suggests cooling (warming) and wetting (drying) over MENA rain-belt region. Moreover, ISM induces a dipole precipitation structure over the tropics caused by ITCZ shift and associated cloud distribution. HiRAM slightly underestimates NAO and ENSO winter cooling over the AP, however; overall patterns are well reproduced. The conducted analysis sheds light on the internal mechanisms of MENA climate variability.
    • Graphene and graphene nanomesh supported nickel clusters: Electronic, magnetic, and hydrogen storage properties

      Fadlallah, M M; Abdelrahman, Ali; Schwingenschlögl, Udo; Maarouf, Ahmed A. (IOP Publishing, 2018-11-05)
      Small-sized nanoparticles are widely used in applications, such as catalysis, nanoelectronics, and hydrogen storage. However, the small size causes a common problem: agglomeration on the support template. One solution is to use templates that limit the mobility of the nanoparticles. Graphene nanomeshes (GNMs) are two dimensional porous structures, with controllably passivated pores. In this work, we employ first principles calculations to investigate the potential for using GNMs as support templates for Ni clusters and, at the same time, study their magnetic and hydrogen storage properties. We consider two Ni clusters (Ni$_{6}$ and Ni$_{13}$) and two GNMs (O-terminated and N-terminated) comparing our results to those of isolated Ni clusters, and those of Ni clusters on graphene. High stability of the Ni clusters is found on the N-GNM in contrast to the O-GNM. We quantify the hydrogen storage capacity by calculating the \n adsorption energy for multiple H$_2$ molecules. The values on Ni$_{x}$/N-GNM are significantly reduced as compared to the corresponding isolated Ni$_{x}$ clusters, but a high hydrogen storage capacity is maintained. The fact that Ni$_{x}$/N-GNM hosts spin polarization is interesting for spintronic applications.
    • Prediction of adsorption isotherms from breakthrough curves

      Poursaeidesfahani, Ali; Andres-Garcia, Eduardo; de Lange, Martijn; Torres-Knoop, Ariana; Rigutto, Marcello; Nair, Nitish; Kapteijn, Freek; Gascon, Jorge; Dubbeldam, David; Vlugt, Thijs J.H. (Elsevier BV, 2018-11-03)
      A mathematical model is used to predict adsorption isotherms from experimentally measured breakthrough curves. Using this approach, by performing only breakthrough experiments for a mixture of two (or more) components, one can obtain pure component adsorption isotherms up to the pressure of the experiment. As a case study, the adsorption of an equimolar mixture of and in zeolite ITQ-29 is investigated. Pure component linear adsorption isotherms for and are predicted by fitting the theoretical breakthrough curves to the experimental ones. Henry coefficients obtained from our approach are in excellent agreement with those measured experimentally. A similar procedure is applied to predict the complete Langmuir adsorption isotherm from breakthrough curves at high pressures. The resulting adsorption isotherms are in very good agreement with those measured experimentally. In our model for transient adsorption, mass transfer from the gas phase to the adsorbed phase is considered using the Linear Driving Force model and dispersion of the gas phase in the packed bed is taken into account. IAST is used to compute the equilibrium loadings for a mixture of gases. The influence of the dispersion coefficient and the effective mass transfer coefficient on the shape of breakthrough curves is investigated and discussed. Rough estimations of these values are sufficient to predict adsorption isotherms from breakthrough curves.
    • Two-to-one internal resonance of an inclined marine riser under harmonic excitations

      Alfosail, Feras; Younis, Mohammad I. (Springer Nature America, Inc, 2018-11-03)
      In this paper, we study the two-to-one internal resonance of an inclined marine riser under harmonic excitations. The riser is modeled as an Euler–Bernoulli beam accounting for mid-plane stretching, self-weight, and an applied axial top tension. Due to the inclination, the self-weight load causes a static deflection of the riser, which can tune the frequency ratio between the third and first natural frequencies near two. The multiple-time-scale method is applied to study the nonlinear equation accounting for the system nonlinearity. The solution is then compared to a Galerkin solution showing good agreement. A further investigation is carried out by plotting the frequency response curves, the force response curves, and the steady-state response of the multiple-time-scale solution, in addition to the dynamical solution obtained by Galerkin, as they vary with the detuning parameters. The results reveal that the riser vibrations can undergo multiple Hopf bifurcations and experience quasi-periodic motion that can lead to chaotic behavior. These phenomena lead to complex vibrations of the riser, which can accelerate its fatigue failure.
    • Effect of seawater-coolant feed arrangement in a waste heat driven multi-stage vacuum membrane distillation system

      Lee, Jung Gil; Bak, Chul-u; Thu, Kyaw; Ghaffour, NorEddine; Kim, Young-Deuk (Elsevier BV, 2018-11-03)
      This paper proposes two types of seawater-coolant feed arrangements of a heat recovery unit (HRU) for improving the performance of a multi-stage vacuum membrane distillation (VMD) system: backward feed (BF) and parallel feed (PF). Theoretical studies were performed to assess the effect of the BF and PF feed arrangements on the system performance. In addition, to comprehensively understand the thermochemical phenomena in both the BF and PF arrangements, spatial variations in the temperature, permeate pressure, permeate flux, and salinity were investigated using a rigorous simulation model that considered the heat and mass transfer across the hollow fibers coupled with the transport behavior on the feed side. To determine the superior HRU configuration between BF and PF, the water production, recovery ratio, and specific energy consumption of the multi-stage VMD system were investigated. It was found that the total water production in the PF arrangement was approximately 2.94 m3/d, which was approximately 6% higher than in the BF arrangement; however, the BF arrangement was more efficient for the production of freshwater than the PF arrangement when a smaller number of module stages was employed. Furthermore, the optimum number of HRUs in the BF arrangement was determined based on this theoretical study.
    • Optimisation of a forward osmosis and membrane distillation hybrid system for the treatment of source-separated urine

      Volpin, F.; Chekli, L.; Phuntsho, S.; Ghaffour, NorEddine; Vrouwenvelder, Johannes S.; Kyong Shon, Ho (Elsevier BV, 2018-11-02)
      The high concentration of nitrogen, phosphorous and potassium in human urine makes it a suitable raw material for fertiliser production. However, urine is often diluted with a significant amount of flushing water which increases the costs for the downstream nutrients recovery process. Re-using the water and the nutrients in the urine is paramount for enhancing the sustainability of our waste management system. In this work, a combination of forward osmosis (FO) and membrane distillation (MD) was used to extract distilled water from human urine. FO was chosen as MD pre-treatment to increase the overall nitrogen rejection and to prevent wetting of the MD membrane. The goal of this investigation was to tune the FO and MD operating parameters to reduce the nitrogen transport to the MD permeate. Urine pH, draw solution (DS) salt concentration and operating pressure were varied as a means to enhance the FO performances. On the other hand, feed temperature, nitrogen concentration and membrane characteristics were investigated to optimise the MD process. With 2.5 M NaCl as DS commercial FO membranes achieved a water flux between 31.5 – 28.7 L.m-2.h-1 and a minimum nitrogen flux of 1.4 g.L-1. An additional 33% reduction in the nitrogen transport was observed by applying minimal hydraulic pressure on the DS. However, this was also found to significantly reduce the net transmembrane water flux. Acidification of the feed was also beneficial for both FO and MD nitrogen rejection. Finally, we demonstrated that, by tuning the MD membrane porosity and thickness, higher MD permeate quality could be achieved. To conclude, the hybrid FO-MD process is expected to be an effective solution for the production of clean water and concentrated fertiliser from human urine. This double barrier separation process could be suitable for both water reclamation in space application and resource recovery in urban application.
    • West African Monsoon: current state and future projections in a high-resolution AGCM

      Raj, Jerry; Bangalath, Hamza Kunhu; Stenchikov, Georgiy L. (Springer Nature America, Inc, 2018-11-02)
      The West African Monsoon (WAM) involves the interaction of multi-scale processes ranging from planetary to cumulus scales, which makes it challenging for coarse resolution General Circulation Models to accurately simulate WAM. The present study evaluates the ability of the high-resolution (∼ 25 km) Atmospheric General Circulation Model HiRAM to simulate the WAM and to analyze its future projections by the end of the 21st century. For the historical period, two AMIP-type simulations were conducted, one forced with observed SST from Hadley Center Sea Ice and Sea Surface Temperature dataset and the other forced with SST from the coarse resolution Earth System Model (ESM2M), which is the parent model of HiRAM, i.e. both models have the same dynamical core and similar physical parameterizations. The future projection, using the Representative Concentration Pathway 8.5 and SST from ESM2M is also conducted. A process-based evaluation is carried out to elucidate HiRAM’s ability to represent the key processes and multiscale dynamic features those define the WAM circulation. Compared to ESM2M, HiRAM better represents most of the key circulation elements at different scales, and thus more accurately represents the intensity and spatial distribution of the WAM rainfall. The position of the African easterly jet is considerably improved in HiRAM simulations, leading to the improved positioning of the WAM rainbelt and the two-cell structure of convection. The future projection of the WAM exhibits warming over the entire domain, decreasing precipitation over the southern Sahel, and increase of precipitation over the western Sahara.
    • Enhancement of the transition to detonation of a turbulent hydrogen–air flame by nanosecond repetitively pulsed plasma discharges

      Gray, Joshua A.T.; Lacoste, Deanna (Elsevier BV, 2018-11-02)
      This work provides proof of concept for the use of nanosecond repetitively pulsed (NRP) plasma discharges to accelerate a propagating turbulent flame, resulting in enhanced deflagration-to-detonation transition and significant reduction in run-up length. The investigations are conducted on a stoichiometric hydrogen-air mixture at near ambient conditions. The effect of plasma actuation on the flame velocity is investigated using time-of-flight measurements of the propagating flame and detonation wave. The flame velocity shortly after the application of the NRP plasma discharges is more than double that obtained in cases in which no plasma is applied. High-speed imaging of OH* chemiluminescence in the electrode area confirms this result and provides insight about the mechanisms of plasma action. While the volumetric energy deposited during plasma actuation is sufficiently low as to not ignite the combustible mixture prior the arrival of the flame, the chemical and thermal enhancement of the gas is efficient enough to significantly accelerate the transition to detonation. The decrease in the run-up length to transition to detonation is obtained for a plasma power of less than 0.14% of the thermal power of the flame. This result indicates that low-energy active devices using NRP discharges might be suitable for replacing passive devices such as orifice plates or Shchelkin spirals.
    • Optimisation of a forward osmosis and membrane distillation hybrid system for the treatment of source-separated urine

      Volpin, F.; Chekli, L.; Phuntsho, S.; Ghaffour, NorEddine; Vrouwenvelder, Johannes S.; Kyong Shon, Ho (Elsevier BV, 2018-11-02)
      The high concentration of nitrogen, phosphorous and potassium in human urine makes it a suitable raw material for fertiliser production. However, urine is often diluted with a significant amount of flushing water which increases the costs for the downstream nutrients recovery process. Re-using the water and the nutrients in the urine is paramount for enhancing the sustainability of our waste management system. In this work, a combination of forward osmosis (FO) and membrane distillation (MD) was used to extract distilled water from human urine. FO was chosen as MD pre-treatment to increase the overall nitrogen rejection and to prevent wetting of the MD membrane. The goal of this investigation was to tune the FO and MD operating parameters to reduce the nitrogen transport to the MD permeate. Urine pH, draw solution (DS) salt concentration and operating pressure were varied as a means to enhance the FO performances. On the other hand, feed temperature, nitrogen concentration and membrane characteristics were investigated to optimise the MD process. With 2.5 M NaCl as DS commercial FO membranes achieved a water flux between 31.5 – 28.7 L.m-2.h-1 and a minimum nitrogen flux of 1.4 g.L-1. An additional 33% reduction in the nitrogen transport was observed by applying minimal hydraulic pressure on the DS. However, this was also found to significantly reduce the net transmembrane water flux. Acidification of the feed was also beneficial for both FO and MD nitrogen rejection. Finally, we demonstrated that, by tuning the MD membrane porosity and thickness, higher MD permeate quality could be achieved. To conclude, the hybrid FO-MD process is expected to be an effective solution for the production of clean water and concentrated fertiliser from human urine. This double barrier separation process could be suitable for both water reclamation in space application and resource recovery in urban application.
    • Structural basis for the recognition of sulfur in phosphorothioated DNA

      Liu, Guang; Fu, Wencheng; Zhang, Zhenyi; He, Yao; Yu, Hao; Wang, Yuli; Wang, Xiaolei; Zhao, Yi-Lei; Deng, Zixin; Wu, Geng; He, Xinyi (Springer Nature America, Inc, 2018-11-02)
      There have been very few reports on protein domains that specifically recognize sulfur. Here we present the crystal structure of the sulfur-binding domain (SBD) from the DNA phosphorothioation (PT)-dependent restriction endonuclease ScoMcrA. SBD contains a hydrophobic surface cavity that is formed by the aromatic ring of Y164, the pyrolidine ring of P165, and the non-polar side chains of four other residues that serve as lid, base, and wall of the cavity. The SBD and PT-DNA undergo conformational changes upon binding. The S187RGRR191 loop inserts into the DNA major groove to make contacts with the bases of the GPSGCC core sequence. Mutating key residues of SBD impairs PT-DNA association. More than 1000 sequenced microbial species from fourteen phyla contain SBD homologs. We show that three of these homologs bind PT-DNA in vitro and restrict PT-DNA gene transfer in vivo. These results show that SBD-like PT-DNA readers exist widely in prokaryotes.
    • Sensitivity Studies of the Red Sea Eddies Using Adjoint Method

      Zhan, Peng; Gopalakrishnan, Ganesh; Subramanian, Aneesh C.; Guo, Daquan; Hoteit, Ibrahim (American Geophysical Union (AGU), 2018-11-01)
      Adjoint sensitivity analysis are applied to a set of eddies in the Red Sea using a high-resolution MITgcm and its adjoint model. Previous studies have reported several eddy events in the Red Sea, namely, a dipole captured on August 17, 2001 in the southern Red Sea, a cyclonic eddy (CE) in November 2011 in the northern Red Sea, and an anticyclonic eddy (AE) in April 2010 in the central Red Sea. Sensitivity analysis is applied here to investigate the governing factors that control the intensity and evolution of these eddies. The eddies are first reproduced by running the MITgcm forward and their sensitivities to external atmospheric forcing and previous model states are then computed using the adjoint model. In the experiments, (relative) surface vorticity (curl of horizontal velocity) are defined as the objective function. The contributions of forcings and model states are quantified and investigated. The sensitivities to external forcings are distinct in different eddy events. The dipole in the central Red Sea is dominantly sensitive to the cross-basin eastward wind jet. The AE in the central Red Sea is most sensitive to the along-basin wind stress. The CE in the northern Red Sea is sensitive to the net heat flux and to surface elevation perturbations even from the remote southern Red Sea, which is attributed to the propagation of baroclinic Kelvin waves along the coast. Analysis of the sensitivity to model state variables suggests that these eddies are also modulated by the boundary currents and the temperature profile distributions.
    • Synthesis and Characterization of Cationic Tetramethyl Tantalum(V) Complex

      Dey, Raju; Mohandas, Janet Chakkamadathil; Samantaray, Manoja; Hamieh, Ali Imad Ali; Kavitake, Santosh Giridhar; Chen, Yin; Abou-Hamad, Edy; Cavallo, Luigi; Poater, Albert; Basset, Jean-Marie (MDPI AG, 2018-11-01)
      A novel method for the synthesis of the homogeneous homoleptic cationic tantalum(V)tetramethyl complex [(TaMe4)+ MeB(C6F5)3−] from neutral tantalumpentamethyl (TaMe5) has been described, by direct demethylation using B(C6F5)3 reagent. The aforesaid higher valent cationic tantalum complex was characterized precisely by liquid state 1H-NMR, 13C-NMR, and 1H-13C-NMR correlation spectroscopy.
    • Macromolecular Brushes by Combination of Ring-Opening and Ring-Opening Metathesis Polymerization. Synthesis, Self-Assembly, Thermodynamics, and Dynamics

      Nikovia, Christiana; Theodoridis, Lazaros; Alexandris, Stelios; Bilalis, Panagiotis; Hadjichristidis, Nikolaos; Floudas, George; Pitsikalis, Marinos (American Chemical Society (ACS), 2018-10-31)
      Statistical and block copolymerization of poly(l-lactide) (PLLA) and poly(ε-caprolactone) (PCL) macromonomers having an end norbornenyl group was performed via ring-opening metathesis polymerization (ROMP) to produce the corresponding statistical and block brush copolymers consisting of PLLA and PCL side chains on a polynorbornene (PNBE) backbone. The molecular characteristics of the macromolecular brushes were determined by 1H NMR spectroscopy and size exclusion chromatography equipped with various detectors. These complex topologies allow addressing important questions on the physics of semicrystalline polymers. These include the role of (i) a doubly grafted PCL or PLLA chain on a NBE moiety (in the macromonomers) and the role of (ii) brush architecture on the crystallization behavior and dynamics of block and statistical copolymers. Significant differences were found between the macromonomers and the corresponding brush copolymers at the crystalline lamellar and spherulitic superstructure levels. In the symmetric brush copolymers, two discrete crystalline lamellae corresponding to PLLA and PCL crystals were formed with that of PNBE–PLLA being thicker as compared to PNBE–PCL. Crystallization of the minority component (PCL) was totally suppressed in the brush copolymers (statistical and block) with asymmetric composition (PLLA–PCL 80–20). These results suggest strong restrictions in the crystallization of the block with the lower crystallization temperature (PCL) as well as confinement effects in the double macromonomers, resulting in lower crystallization and melting temperatures. At the level of spherulitic superstructure, NBE–PCL and NBE–(PCL)2 form the usual spherulites with growth rates that are dominated by the segmental dynamics. On the other hand, NBE–PLLA forms normal spherulites at low temperatures that transform to banded spherulites at higher temperatures. NBE–(PLLA)2 forms banded spherulites over the whole temperature range. A common feature of PLLA macromonomers is the nearly temperature-independent growth rates around 30 K, reflecting a property of the segmental dynamics. In the brush copolymers with symmetric composition both PLLA (in banded spherulites) and PCL could crystallize. PCL crystallization initiated at the same nucleation sites that crystallized PLLA at higher temperatures.