Enhanced mass transport in graphene nanofluidic channels

Enhanced mass transport in carbon-based nanoscale conduits (e.g. carbon nanotubes, graphene nanochannels/capillaries, graphene/graphene oxide membranes) has attracted tremendous interest over the last decade due to its significant implications for water desalination/purification, nanofiltration, electronic cooling, battery/fuel cells, and lab-on-a-chip. Further development of carbon-based nanoscale conduits for practical applications relies on understanding fundamental mechanisms of transport through individual conduits, which have not been well studied due to challenges in fabrication and measurement. In this thesis, the construction of two-dimensional planar graphene nanochannel devices and the studies of enhanced water and ion transport inside the graphene nanochannels are reported for the first time. The graphene nanochannels are fabricated by conformally covering high-quality graphene on the surfaces of silica nanochannels. A new fabrication scheme consisting of graphene wet transfer, graphene patterning and vacuum anodic bonding is developed to create such graphene nanochannels with heights ranging from 24 to 124 nm. Using these nanochannels and a new hybrid nanochannel based capillary flow measurement technique, we successfully measured the hydraulic resistance (water permeability) of single graphene nanochannels. Our results demonstrate that the frictionless surface of graphene induces a boundary slip and enhances water flow inside the graphene nanochannel. The measured slip length of graphene in the graphene nanochannels poses a median value around 16 nm, albeit with a large variation from 0 to 200 nm regardless of the channel height. The small-yet-widely-varying values of the graphene slip length are attributed to the surface charge of graphene and the interaction between graphene and underneath silica substrate, which are in good agreement with the prediction of our molecular dynamics (MD) simulation. In addition, we also investigated enhanced ion transport inside the graphene nanochannels. Higher electroosmotic conductance at low electrolyte concentrations (10-6 M~10-2 M) is observed in graphene nanochannels when compared with silica nanochannels with the same geometry. Our results suggest that the enhanced electroosmotic flow is also due to the boundary slip at the graphene/electrolyte interface. Besides, our analysis shows that the surface charge on the graphene, originating from the dissociation of oxygen-containing functional groups, is crucial to the enhanced electroosmotic flow inside nanochannels

First-principles Study of High-Pressure Phase Stability and Superconductivity of Bi4I4

Bismuth iodide Bi4I4 exhibits intricate crystal structures and topological insulating states that are highly susceptible to influence by environments, making its physical properties highly tunable by external conditions. In this work, we study the evolution of structural and electronic properties of Bi4I4 at high pressure using an advanced structure search method in conjunction with first-principles calculations. Our results indicate that the most stable ambient-pressure monoclinic α−Bi4I4 phase in C2/m symmetry transforms to a trigonal P31c structure (ɛ−Bi4I4) at 8.4 GPa, then to a tetragonal P4/mmm structure (ζ−Bi4I4) above 16.6 GPa. In contrast to the semiconducting nature of ambient-pressure Bi4I4, the two high-pressure phases are metallic, in agreement with reported electrical measurements. The ɛ−Bi4I4 phase exhibits distinct ionic states of Iδ− and (Bi4I3)δ + (δ=0.4123 e), driven by a pressure-induced volume reduction. We show that both ɛ- and ζ−Bi4I4 are superconductors, and the emergence of pressure-induced superconductivity might be intimately linked to the underlying structural phase transitions

Exploring the Persuasion Effects of Threatening Content in COVID-19 Advertising: The Roles of Threat Intensity and Sensation Seeking on Consumer Attitudes

The COVID-19 pandemic has resulted in a wave of advertising activities advocating care for the community in a time of crisis. These COVID-19 ads often feature threatening depictions of the crisis as a persuasion strategy. Hence, the present study explores the persuasion effects of COVID-19 advertising by focusing on threat persuasion. Specifically, by adopting an online experiment with 724 U.S. participants, this study investigates how the threat intensity of crisis depictions featured in COVID-19 ads (low vs. medium vs. high) interact with individual differences in sensation-seeking in order to impact ads and brand attitudes, through the mediating pathways of positive moral emotions (warmth and gratitude) and corporate social responsibility (CSR) authenticity. The results reveal that the high-threat crisis depiction generates the lowest warmth and ad attitudes, whereas the medium-threat crisis depiction yields the strongest gratitude and better brand attitudes than the low-threat crisis depiction, but only for low sensation seekers (LSS). Also, for LSS, exposure to the medium-threat (versus low-threat) crisis depiction increases their gratitude, which leads to higher CSR authenticity, and, eventually results in more favorable ad or brand attitudes. On the contrary, for high sensation seekers, threat intensity does not have an indirect effect on the ad or brand attitudes via warmth, gratitude, and CSR authenticity

Preanthesis biomass accumulation of plant and plant organs defines yield components in wheat

The preanthesis period in wheat is critical for growth of plant organs including leaves, stems, spikes and roots. However, the roles of the preanthesis biomass accumulation of plant and plant organs in yield determination are only partially elucidated, and the underlying genetic basis remains largely unknown. This study aimed to understand the physiological and genetic relationships between preanthesis biomass accumulation and yield determination. In a mapping population of bread wheat (Triticum aestivum ‘Forno’) and its relative spelt (Triticum spelta ‘Oberkulmer’) contrasting for biomass, the dry weight of above-ground whole shoots and different organs, and leaf area, were analysed at GS39 (full flag leaf emergence) and anthesis. Yield components (thousand grain weight, grains per spike, final shoot biomass and grain weight per spike) and plant height were measured at maturity, followed by identification of quantitative trait loci (QTL) for all above traits. Field experiments were carried out in UK in 2011–2012 and 2012–2013 seasons, each using a randomised complete block design with three replicates. The results showed that there was a significant variation in biomass and its partitioning to organs at different stages. Consistent with the previous findings, stem water soluble carbohydrates and spike dry weight at anthesis contributed to thousand grain weight and grains per spike, respectively. In addition, this study revealed many other traits positively associated with one or more yield components, including biomass and leaf area at GS39, leaf and structural stem growth as well as whole shoot biomass at anthesis, and higher dry matter accumulation and crop (and spike) growth rates between the two stages. Increasing shoot biomass by removing other tillers at GS39 led to higher grain number and grain weight per spike. These results indicate the importance of the preanthesis growth of plant and plant organs for yield determination. Plant height was only weakly correlated with final biomass at maturity so it is possible to produce high-biomass genotypes without increasing plant height. Genetic analysis revealed 193 QTL associated with biomass and biomass-related traits. Frequent QTL coincidences between biomass and yield traits were observed, mainly on chromosomes 2B, 3A, 4A, 4B, 5A, 6A and 7B, indicating pleiotropy or tight gene linkages, consistent with their phenotypic associations. The preanthesis biomass traits associated with yield components and the underlying QTL, would facilitate the trait-based physiological and molecular breeding in wheat

Physiological and genetic determination of yield and yield components in a bread wheat × spelt mapping population

A substantial increase in wheat yield is needed for global food security. This requires a comprehensive understanding of the physiological and genetic basis of yield determination. The present study aimed to dissect yield physiologically and genetically in a recombinant inbred line mapping population derived from bread wheat × spelt. A total of 201 traits were investigated in the field and glasshouse across three years, and these traits formed five themes: genetic variation in yield and yield components, and the usefulness of spelt as a genetic resource; tillering dynamics; biomass accumulation; flowering time and subsequent leaf senescence; and grain filling processes. Large genetic variation in all traits was found, and spelt showed many desirable traits and alleles independent of low threshability, so it can be used to broaden genetic diversity for yield improvement in bread wheat, while maintaining the free-threshing habit. Quantitative trait loci for tiller production and survival were identified, which were also affected by light environment under the canopy: low red:far red ratio (R:FR) led to early tillering cessation, few total shoots, high infertile shoot number and shoot abortion, probably resulting from an assimilate shortage due to early and enhanced stem growth induced by low R:FR. More fertile tillers normally contributed to plant yield and grain number, but reduced individual grain weight, partly because of smaller carpels and fewer stem water soluble carbohydrates at anthesis. In addition, preanthesis biomass accumulation increased yield and yield components. For grain weight, slightly early anthesis and delayed but fast leaf senescence were associated with larger grains. Carpel size at anthesis, grain dry matter and water accumulation, as well as grain morphological expansion, determined final grain weight, because of pleiotropy or tight gene linkages. These findings provide deeper insight into yield determination in wheat, and facilitate trait-based physiological and molecular breeding

Generalized quaternion groups with the mm-DCI property

A Cayley digraph Cay(G,S) of a finite group $G$ with respect to a subset $S$ of $G$ is said to be a CI-digraph if for every Cayley digraph Cay(G,T) isomorphic to Cay(G,S), there exists an automorphism $\sigma$ of $G$ such that $S^\sigma=T$. A finite group $G$ is said to have the $m$-DCI property for some positive integer $m$ if all $m$-valent Cayley digraphs of $G$ are CI-digraphs, and is said to be a DCI-group if $G$ has the $m$-DCI property for all $1\leq m\leq |G|$. Let $\mathrm{Q}_{4n}$ be a generalized quaternion group of order $4n$ with an integer $n\geq 3$, and let $\mathrm{Q}_{4n}$ have the $m$-DCI property for some $1 \leq m\leq 2n-1$. It is shown in this paper that $n$ is odd, and $n$ is not divisible by $p^2$ for any prime $p\leq m-1$. Furthermore, if $n\geq 3$ is a power of a prime $p$, then $\mathrm{Q}_{4n}$ has the $m$-DCI property if and only if $p$ is odd, and either $n=p$ or $1\leq m\leq p$.Comment: 1