Hydrogen Storage in Partially Exfoliated Magnesium Diboride Multilayers

Metal boride nanostructures have shown significant promise for hydrogen storage applications. However, the synthesis of nanoscale metal boride particles is challenging because of their high surface energy, strong inter- and intraplanar bonding, and difficult-to-control surface termination. Here, it is demonstrated that mechanochemical exfoliation of magnesium diboride in zirconia produces 3–4 nm ultrathin MgB₂ nanosheets (multilayers) in high yield. High-pressure hydrogenation of these multilayers at 70 MPa and 330 °C followed by dehydrogenation at 390 °C reveals a hydrogen capacity of 5.1 wt%, which is ≈50 times larger than the capacity of bulk MgB₂ under the same conditions. This enhancement is attributed to the creation of defective sites by ball-milling and incomplete Mg surface coverage in MgB₂ multilayers, which disrupts the stable boron–boron ring structure. The density functional theory calculations indicate that the balance of Mg on the MgB₂ nanosheet surface changes as the material hydrogenates, as it is energetically favorable to trade a small number of Mg vacancies in Mg(BH₄)₂ for greater Mg coverage on the MgB₂ surface. The exfoliation and creation of ultrathin layers is a promising new direction for 2D metal boride/borohydride research with the potential to achieve high-capacity reversible hydrogen storage at more moderate pressures and temperatures.     

Low-Complexity Selected Mapping Scheme Using a Bank of Butterfly Circuits in Orthogonal Frequency Division Multiplexing Systems

Selected mapping schemes (SLMs) have gained popularity to improve the peak-to-average power ratio (PAPR) reduction performance. Even so, the computational load increases greatly owing to the many inverse fast Fourier transforms (IFFTs) in conventional SLM (CSLM) and to overcome this disadvantage, several low-complexity schemes are in vogue. This paper proposes two \(\frac{N}{2}\)-point IFFTs, where N is the number of subcarriers in OFDM, and a bank of butterfly circuits (BFCs) to replace multiple IFFTs in the CSLM. The output sequence of the two \(\frac{N}{2}\)-point IFFTs are simultaneously sent to a bank of M-BFCs to generate a set of M statistically independent candidate signals, including the original OFDM signal. The parameters of the first BFC, which generates the original OFDM signal, are derived. To simplify the complexity, constraints are imposed on the selection of parameters of the remaining M ? 1 BFCs. The results indicate that the proposed SLM (PSLM), when compared with the CSLM, achieves an appreciable computational complexity reduction gain with the loss of a slight PAPR reduction performance.     

Food compatibility and degradation properties of pro‐oxidant‐loaded LLDPE film

To avoid environmental hazards, packaging industries are aiming to produce biodegradable films for food contact safety and its degradation. LLDPE film containing 1% pro‐oxidant additive was studied for food compatibility in different simulants, at room temperature conditions as per Bureau of Indian Standards (BIS), code of federal regulations (CFR), food and drug administration USA (USFDA), and European Economic Commission directives (EEC) specifications. Overall migration values were well within the specified limits for food contact applications at room temperature filling and storing. The pro‐oxidant loaded LLDPE film was also studied for its degradation behavior with the changes in physical and mechanical properties along with thermal behavior, morphology and infrared spectroscopy. The molecular oxidations of pro‐oxidant‐loaded LLDPE films are severed which increases hydrophilicity. Evidently, the oxidation renders the material much more vulnerable to microbial attack. The combined effect of both photo and bio degradation is most effective for complete degradation of film. The results obtained from these studies revealed that the fine balance (1%) of pro‐oxidant contents in the film guarantees food contact safety and its degradation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39756.     

Dietary Berries and Ellagic Acid Prevent Oxidative DNA Damage and Modulate Expression of DNA Repair Genes

DNA damage is a pre-requisite for the initiation of cancer and agents that reduce this damage are useful in cancer prevention. In this study, we evaluated the ability of whole berries and berry phytochemical, ellagic acid to reduce endogenous oxidative DNA damage. Ellagic acid was selected based on >95% inhibition of 8-oxodeoxyguosine (8-oxodG) and other unidentified oxidative DNA adducts induced by 4-hydroxy-17ß-estradiol and CuCl₂ in vitro. Inhibition of the latter occurred at lower concentrations (10 μM) than that for 8-oxodG (100 μM). In the in vivo study, female CD-1 mice (n=6) were fed either a control diet or diet supplemented with ellagic acid (400 ppm) and dehydrated berries (5% w/w) with varying ellagic acid contents – blueberry (low), strawberry (medium) and red raspberry (high), for 3 weeks. Blueberry and strawberry diets showed moderate reductions in endogenous DNA adducts (25%). However, both red raspberry and ellagic acid diets showed a significant reduction of 59% (p < 0.001) and 48% (p < 0.01), respectively. Both diets also resulted in a 3–8 fold over-expression of genes involved in DNA repair such as xeroderma pigmentosum group A complementing protein (XPA), DNA excision repair protein (ERCC5) and DNA ligase III (DNL3). These results suggest that red raspberry and ellagic acid reduce endogenous oxidative DNA damage by mechanisms which may involve increase in DNA repair.     

Influence of molecular dipole on monoacrylate monomer reactivity

Numerous acrylate monomers have been synthesized and evaluated extensively as a means to explore the relationship between molecular polarity and monomer reactivity. Various monomers, characterized by high values of dipole moment, were polymerized in bulk, and no correlation of dipole moment to monomer reactivity was established. Solution polymerization studies were performed on phenyl carbamate ethyl acrylate and several substituted derivatives to observe the effects of changing solvent polarity on the polymerization kinetics. The results of solution polymerization studies indicated that traditional dilution effects, which suppress the polymerization kinetics, dominate the reactions. Changes in solvent polarity had minimal impact on the polymerization kinetics.     

Remote sensing of invasive plants: incorporating functional traits into the picture

Invasive plant species spread presents a challenge, requiring better mapping and monitoring for control. Remote sensing (RS) provides an efficient tool to map invasive plants in diverse ecosystems. Yet applications of RS for invasive plant mapping largely rely on spatial and spectral patterns. The use of invasive plant functional traits can improve RS mapping, using ecological insights on processes and functions associated with invasion. We summarize research utilizing plant functional traits in RS mapping of invasive species from the years 2000 to 2014. Based on this review, we summarize plant traits that can be related to spatial and spectral properties, and used to discriminate invasive alien plants from native vegetation. Phenological and structural plant traits have been relatively well exploited via RS for invasion studies. In comparison, there has been limited utilization of physiological traits (with the exception of properties such as nitrogen content). This is an area that merits further research attention, via the linkage of ecophysiological field research with RS.     

Supramolecular β‐Sheet Suckerin–Based Underwater Adhesives

Nature has evolved several molecular strategies to ensure adhesion in aqueous environments, where artificial adhesives typically fail. One recently‐unveiled molecular design for wet‐resistant adhesion is the cohesive cross‐β structure characteristic of amyloids, complementing the well‐established surface‐binding strategy of mussel adhesive proteins based on 3,4‐l ‐dihydroxyphenylalanine (Dopa). Structural proteins that self‐assemble into cross β‐sheet networks are the suckerins discovered in the sucker ring teeth of squids. Here, light is shed on the wet adhesion of cross‐β motifs by producing recombinant suckerin‐12, naturally lacking Dopa, and investigating its wet adhesion properties. Surprisingly, the adhesion forces measured on mica reach 70 mN m^?1, exceeding those measured for all mussel adhesive proteins to date. The pressure‐sensitive adhesion of artificial suckerins is largely governed by their cross‐β motif, as evidenced using control experiments with disrupted cross‐β domains that result in complete loss of adhesion. Dopa is also incorporated in suckerin‐12 using a residue‐specific incorporation strategy that replaces tyrosine with Dopa during expression in Escherichia coli. Although the replacement does not increase the long‐term adhesion, it contributes to the initial rapid contact and enhances the adsorption onto model oxide substrates. The findings suggest that suckerins with supramolecular cross‐β motifs are promising biopolymers for wet‐resistant adhesion.     

Performance Evaluation of a Multi-Robot Search & Retrieval System: Experiences with MinDART

Swarm techniques, where many simple robots are used instead of complex ones for performing a task, promise to reduce the cost of developing robot teams for many application domains. The challenge lies in selecting an appropriate control strategy for the individual units. This work explores the effect of control strategies of varying complexity and environmental factors on the performance of a team of robots at a foraging task when using physical robots (the Minnesota Distributed Autonomous Robotic Team). Specifically we study the effect of localization and of simple indirect communication techniques on task completion time using two sets of foraging experiments. We also present results for task performance with varying team sizes and target distributions. As indicated by the results, control strategies with increasing complexity reduce the variance in the performance, but do not always reduce the time to complete the task.