Effects of conformation on the electronic and optical properties of aryleneethynylenes

Materials based upon the aryleneethynylene skeleton are currently of great interest. The fluorescent and electroluminescent properties of both molecular and polymeric systems has prompted speculation about the suitability of these materials as the emitting layer in electroluminescent devices, while the conjugated π-system has led to the development of molecular wire-like architectures, and materials which display negative differential resistance. The degree of conjugation in the π-system is dependent on the relative orientation of the aromatic rings. The barrier to rotation about the aryl-alkynyl single bond for phenyleneethynylenes is very low, leading to a continuum of rotational isomers when in solution. Engineering physical control over the conformation of aryleneethynylenes therefore presents a significant challenge. In this work, a review is presented on the uses, behaviour and synthesis of aryleneethynylenes, followed by an account of the practical work carried out. Initially various series of 1,4-bis(phenylethynyl)benzene (BPEB) analogues containing naphthalene and thiophene moieties were produced. Study of the photophysical behaviour and molecular modelling of these systems suggests that the choice of central ring in a three ring aryleneethynylene system has the greatest effect on the compounds’ characteristics. This can be attributed to the π-electrons of the central aromatic ring giving the largest contribution to the frontier orbitais of these compounds. Conformational control of aryleneethynylenes is then examined. Derivatives of BPEB and 9,10-bis(phenylethynyl)anthracene (BPEA) with bulky alkyl substituents have been synthesised, with the aim of using steric bulk to restrict rotation about the acetylenie bond. Initial attempts at this approach resulted in the additional steric bulk only giving slight conformational restriction in the solid state as well as only having a small effect on the observed photophysics. Subsequently, compounds were successfully synthesised where, in the ground state, the two outer rings were orthogonal to the central ring system, switching off their contribution to the frontier orbitais, and thus leading to significant changes in photophysical behaviour being observed relative to BPEB and BPEA

Constrained Planarity in Practice -- Engineering the Synchronized Planarity Algorithm

In the constrained planarity setting, we ask whether a graph admits a planar drawing that additionally satisfies a given set of constraints. These constraints are often derived from very natural problems; prominent examples are Level Planarity, where vertices have to lie on given horizontal lines indicating a hierarchy, and Clustered Planarity, where we additionally draw the boundaries of clusters which recursively group the vertices in a crossing-free manner. Despite receiving significant amount of attention and substantial theoretical progress on these problems, only very few of the found solutions have been put into practice and evaluated experimentally. In this paper, we describe our implementation of the recent quadratic-time algorithm by Bl\"asius et al. [TALG Vol 19, No 4] for solving the problem Synchronized Planarity, which can be seen as a common generalization of several constrained planarity problems, including the aforementioned ones. Our experimental evaluation on an existing benchmark set shows that even our baseline implementation outperforms all competitors by at least an order of magnitude. We systematically investigate the degrees of freedom in the implementation of the Synchronized Planarity algorithm for larger instances and propose several modifications that further improve the performance. Altogether, this allows us to solve instances with up to 100 vertices in milliseconds and instances with up to 100 000 vertices within a few minutes.Comment: to appear in Proceedings of ALENEX 202

Experimental Comparison of PC-Trees and PQ-Trees

PQ-trees and PC-trees are data structures that represent sets of linear and circular orders, respectively, subject to constraints that specific subsets of elements have to be consecutive. While equivalent to each other, PC-trees are conceptually much simpler than PQ-trees; updating a PC-tree so that a set of elements becomes consecutive requires only a single operation, whereas PQ-trees use an update procedure that is described in terms of nine transformation templates that have to be recursively matched and applied. Despite these theoretical advantages, to date no practical PC-tree implementation is available. This might be due to the original description by Hsu and McConnell [Hsu et al., 2003] in some places only sketching the details of the implementation. In this paper, we describe two alternative implementations of PC-trees. For the first one, we follow the approach by Hsu and McConnell, filling in the necessary details and also proposing improvements on the original algorithm. For the second one, we use a different technique for efficiently representing the tree using a Union-Find data structure. In an extensive experimental evaluation we compare our implementations to a variety of other implementations of PQ-trees that are available on the web as part of academic and other software libraries. Our results show that both PC-tree implementations beat their closest fully correct competitor, the PQ-tree implementation from the OGDF library [Markus Chimani et al., 2014; Leipert, 1997], by a factor of 2 to 4, showing that PC-trees are not only conceptually simpler but also fast in practice. Moreover, we find the Union-Find-based implementation, while having a slightly worse asymptotic runtime, to be twice as fast as the one based on the description by Hsu and McConnell

Synchronized planarity with applications to constrained planarity problems

We introduce the problem Synchronized Planarity. Roughly speaking, its input is a loop-free multi-graph together with synchronization constraints that, e.g., match pairs of vertices of equal degree by providing a bijection between their edges. Synchronized Planarity then asks whether the graph admits a crossing-free embedding into the plane such that the orders of edges around synchronized vertices are consistent. We show, on the one hand, that Synchronized Planarity can be solved in quadratic time, and, on the other hand, that it serves as a powerful modeling language that lets us easily formulate several constrained planarity problems as instances of Synchronized Planarity. In particular, this lets us solve Clustered Planarity in quadratic time, where the most efficient previously known algorithm has an upper bound of O(n⁸)

Parameterized Complexity of Simultaneous Planarity

Given $k$ input graphs $G_1, \dots ,G_k$, where each pair $G_i$, $G_j$ with $i \neq j$ shares the same graph $G$, the problem Simultaneous Embedding With Fixed Edges (SEFE) asks whether there exists a planar drawing for each input graph such that all drawings coincide on $G$. While SEFE is still open for the case of two input graphs, the problem is NP-complete for $k \geq 3$ [Schaefer, JGAA 13]. In this work, we explore the parameterized complexity of SEFE. We show that SEFE is FPT with respect to $k$ plus the vertex cover number or the feedback edge set number of the the union graph $G^\cup = G_1 \cup \dots \cup G_k$. Regarding the shared graph $G$, we show that SEFE is NP-complete, even if $G$ is a tree with maximum degree 4. Together with a known NP-hardness reduction [Angelini et al., TCS 15], this allows us to conclude that several parameters of $G$, including the maximum degree, the maximum number of degree-1 neighbors, the vertex cover number, and the number of cutvertices are intractable. We also settle the tractability of all pairs of these parameters. We give FPT algorithms for the vertex cover number plus either of the first two parameters and for the number of cutvertices plus the maximum degree, whereas we prove all remaining combinations to be intractable.Comment: Appears in the Proceedings of the 31st International Symposium on Graph Drawing and Network Visualization (GD 2023

The applicability of a validated team-based learning student assessment instrument to assess United Kingdom pharmacy students' attitude toward team-based learning

Purpose It aimed at testing the validity and reliability of a validated team-based learning student assessment instrument (TBL-SAI) to assess United Kingdom pharmacy students’ attitude toward TBL. Methods TBL-SAI, consisting of 33 items, was administered to undergraduate pharmacy students from two schools of pharmacy each at University of Wolverhampton and University of Bradford were conducted on the data, along with comparison between the two schools. Results Students’ response rate was 80.0% (138/173) in completion of the instrument. Overall, the instrument demonstrated validity and reliability when used with pharmacy students. Sub-analysis between schools of pharmacy did, however, show that four items from Wolverhampton data, had factor loadings of less than 0.40. No item in the Bradford data had factor loadings less than 0.40. Cronbach’s alpha score was reliable at 0.897 for the total instrument: Wolverhampton, 0.793 and Bradford, 0.902. Students showed preference to TBL, with Bradford’s scores being statistically higher (P<0.005). Conclusion This validated instrument has demonstrated reliability and validity when used with pharmacy students. Furthermore students at both schools preferred TBL compared to traditional teaching

Winter beans: the use of an unmanned aerial vehicle for monitoring and prediction of crop performance

Traditional field-based techniques for phenotyping of crops are based on visual assessment which are subjective and time consuming. A high throughput automated technique using an unmanned aerial vehicle (UAV) with a multispectral image (MSI) camera was used to investigate the correlation between markers of winter bean crop development with eventual crop yield. A simplified approach has been developed using different vegetation indices i.e. NDVI, GNDVI and NDRE, coupled with an iso-cluster classification method to monitor plant characteristics across all growing stages. The UAV-MSI data could then be incorporated into a yield estimator model to estimate the winter bean seed yield.  The NDVI approach showed the greatest correlation between the modelled seed yield and the actual seed yield determined on two separate occasions (R2 = 0.84 and R2 = 0.87). In addition, GNDVI and NDRE were a better estimator of seed yield for areas with dense vegetation. These are hence shown to be able to monitor a winter bean harvest in an efficient and timely manner

Fourier Transform Scanning Tunneling Spectroscopy: the possibility to obtain constant energy maps and the band dispersion using a local measurement

We present here an overview of the Fourier Transform Scanning Tunneling spectroscopy technique (FT-STS). This technique allows one to probe the electronic properties of a two-dimensional system by analyzing the standing waves formed in the vicinity of defects. We review both the experimental and theoretical aspects of this approach, basing our analysis on some of our previous results, as well as on other results described in the literature. We explain how the topology of the constant energy maps can be deduced from the FT of dI/dV map images which exhibit standing waves patterns. We show that not only the position of the features observed in the FT maps, but also their shape can be explained using different theoretical models of different levels of approximation. Thus, starting with the classical and well known expression of the Lindhard susceptibility which describes the screening of electron in a free electron gas, we show that from the momentum dependence of the susceptibility we can deduce the topology of the constant energy maps in a joint density of states approximation (JDOS). We describe how some of the specific features predicted by the JDOS are (or are not) observed experimentally in the FT maps. The role of the phase factors which are neglected in the rough JDOS approximation is described using the stationary phase conditions. We present also the technique of the T-matrix approximation, which takes into account accurately these phase factors. This technique has been successfully applied to normal metals, as well as to systems with more complicated constant energy contours. We present results recently obtained on graphene systems which demonstrate the power of this technique, and the usefulness of local measurements for determining the band structure, the map of the Fermi energy and the constant-energy maps.Comment: 33 pages, 15 figures; invited review article, to appear in Journal of Physics D: Applied Physic

***TEST SUBMISSION*** BMJ-15: Acceptance within last 3 months (01/03/2020); Online publication within 12 months (10/12/2020); Embargo (10/09/2021) less than 12 months from pub date; VoR

From UAT Test publisher via Jisc Publications RouterHistory: accepted 2020-03-01, epub 2020-12-10Article version: VoRPublication status: PublishedAbstract: TEST: THIS IS A PUBLICATIONS ROUTER TEST SUBMISSION. Objectives: To quantify post-colonoscopy colorectal cancer (PCCRC) rates in England by using recent World Endoscopy Organisation guidelines, compare incidence among colonoscopy providers, and explore associated factors that could benefit from quality improvement initiatives. Design: Population based cohort study. Setting: National Health Service in England between 2005 and 2013. Population: All people undergoing colonoscopy and subsequently diagnosed as having colorectal cancer up to three years after their investigation (PCCRC-3yr). Main outcome measures: National trends in incidence of PCCRC (within 6-36 months of colonoscopy), univariable and multivariable analyses to explore factors associated with occurrence, and funnel plots to measure variation among providers. Results: The overall unadjusted PCCRC-3yr rate was 7.4% (9317/126 152), which decreased from 9.0% in 2005 to 6.5% in 2013 (P<0.01). Rates were lower for colonoscopies performed under the NHS bowel cancer screening programme (593/16 640, 3.6%), while they were higher for those conducted by non-NHS providers (187/2009, 9.3%). Rates were higher in women, in older age groups, and in people with inflammatory bowel disease or diverticular disease, in those with higher comorbidity scores, and in people with previous cancers. Substantial variation in rates among colonoscopy providers remained after adjustment for case mix. Conclusions: Wide variation exists in PCCRC-3yr rates across NHS colonoscopy providers in England. The lowest incidence was seen in colonoscopies performed under the NHS bowel cancer screening programme. Quality improvement initiatives are needed to address this variation in rates and prevent colorectal cancer by enabling earlier diagnosis, removing premalignant polyps, and therefore improving outcomes