Investigations of Triplet-Pair States in π-Conjugated Singlet Fission Materials

Singlet fission is the process by which a singlet exciton splits into two ‘free’ triplet excitons. This was the definition of singlet fission up to the last few years when advances in the understanding of singlet fission in acene and heteroacene materials sparked a change in nomenclature in the field. Techniques such as electron paramagnetic resonance spectroscopy have allowed researchers to improve the understanding of singlet fission by visualizing the intermediate states in the singlet fission process. Currently in acene literature, it is common for the initial step of a singlet exciton converting to a singlet character triplet-pair state to be considered singlet fission. This change has interesting ramifications when it is applied to polyenes, another class of singlet fission material, where internal conversion from the absorbing state is thought to occur to a singlet state of triplet-pair character. We contribute to the above discussion by investigating the intermediate triplet-pair states in three systems using innovative techniques. We start by investigating the well-studied TIPS-tetracene system using strong light-matter coupling to manipulate the character of the intermediate states. The results here point to a whole field of research, manipulating state energies and radiative character to enhance triplet-fed emission. In Chapters 5 and 6 we investigate the question posed above by studying two polyene systems. First, we measure a series of oligo(thienylene-vinylenes) which allow us to study the conjugation length dependence of singlet fission. Then in the final chapter we use an exciting new design philosophy of man-made proteins to form carotenoid aggregates. Through this chapter we are able to show experimental evidence for the triplet-pair nature of the 2Ag- singlet state in polyenes. Furthermore, we find the surprising result that singlet fission is incredibly robust in carotenoid aggregates being invariant with protein environment and intramolecular structure. We finish by discussing the implications of the results presented here and point to possible future avenues to further demystify the decay processes of singlet fission materials

Highway Infrastructure Investment and Regional Employment Growth: Dynamic Panel Regression Analysis

A number of macro-level studies attempting to establish the statistical link between public investment in highway infrastructure and employment have applied econometric techniques to estimate the effect of highways while controlling for the effects associated with other factors. Unfortunately, direct use of empirical findings from these historic and recent studies, in shaping transport policy and supporting particular investment decisions, has been rather limited by mixed and inconclusive evidence in the literature. Apart from the common differences among these studies in scope and methodology, another possible reason for the contradictory evidence is that much of the previous work has generally suffered from several methodology drawbacks. In many studies, for instance, several important determinants of employment growth are omitted, and the choices of control variables included in the estimated equations generally are not based on theory. Those studies based solely on cross-sectional data also typically do not account for unobserved regional heterogeneity that may explain spatial differences in employment changes. Moreover, the possibility that the causal relationship between transportation investment and economic growth could work in both directions is generally ignored. This paper attempts to shed some light on this controversy by analysing the effect of highway investment on county-level employment in the State of North Carolina, United States. We derive a reduced from model of equilibrium employment that considers the effects of highways and other potential factors on the supply and demand for labour. Given the potential for lagged responses of the labour market to any exogenous shock, we assume a partial adjustment process for actual employment in our empirical model. A panel data set for 100 North Carolina counties from 1985 to 1997 is used in order to control for unobserved county and time specific effects using panel regression techniques. We also address the causality issue by the use of a two-stage least squares procedure with an instrumental variable. Our main results are that the employment effect of highway infrastructure depends critically on model specifications considered, and failure to account for the dynamics of employment adjustment could lead to an upward bias in the estimated effect of highways.

New lower bounds on crossing numbers of Km,nK_{m,n} from semidefinite programming

In this paper, we use semidefinite programming and representation theory to compute new lower bounds on the crossing number of the complete bipartite graph $K_{m,n}$, extending a method from de Klerk et al. [SIAM J. Discrete Math. 20 (2006), 189--202] and the subsequent reduction by De Klerk, Pasechnik and Schrijver [Math. Prog. Ser. A and B, 109 (2007) 613--624]. We exploit the full symmetry of the problem using a novel decomposition technique. This results in a full block-diagonalization of the underlying matrix algebra, which we use to improve bounds on several concrete instances. Our results imply that $\text{cr}(K_{10,n}) \geq 4.87057 n^2 - 10n$, $\text{cr}(K_{11,n}) \geq 5.99939 n^2-12.5n$, $\text{cr}(K_{12,n}) \geq 7.25579 n^2 - 15n$, $\text{cr}(K_{13,n}) \geq 8.65675 n^2-18n$ for all $n$. The latter three bounds are computed using a new and well-performing relaxation of the original semidefinite programming bound. This new relaxation is obtained by only requiring one small matrix block to be positive semidefinite.Comment: 17 pages, 3 figures, 3 tables. Revisions have been made based on comments of the referees. Accepted for publication in Mathematical Programmin

P-critical integral quadratic forms and positive unit forms: An algorithmic approach

AbstractWe introduce the class of P-critical integral unit forms q:Zn→Z containing the critical forms in the sense of Ovsienko [13]. Several characterisations of P-critical forms are given. In particular, it is proved that q is P-critical if and only if there is a uniquely determined extended Dynkin diagram Δ∈{A∼n,D∼n,E∼6,E∼7,E∼8} and a special group isomorphism T:Zn→Zn such that q∘T is the quadratic form qΔ:Zn→Z,n=|Δ0|, of the diagram Δ. A correspondence between positive forms p:Zn-1→Z with a sincere root and P-critical forms q:Zn→Z is described and efficient linear algebra algorithms for computing P-critical unit forms and positive forms are constructed

Polygonal complexes

Ian Leary inquires whether a class of hyperbolic finitely presented groups are residually finite. We answer in the affirmative by giving a systematic version of a construction in his paper, which shows that the standard 2-complexes of these presentations have a VH-structure. This structure induces a splitting of these groups, which together with hyperbolicity, implies that these groups are residually finite

Elastic effects of vacancies in strontium titanate: Short- and long-range strain fields, elastic dipole tensors, and chemical strain

We present a study of the local strain effects associated with vacancy defects in strontium titanate and report the first calculations of elastic dipole tensors and chemical strains for point defects in perovskites. The combination of local and long-range results will enable determination of x-ray scattering signatures that can be compared with experiments. We find that the oxygen vacancy possesses a special property -- a highly anisotropic elastic dipole tensor which almost vanishes upon averaging over all possible defect orientations. Moreover, through direct comparison with experimental measurements of chemical strain, we place constraints on the possible defects present in oxygen-poor strontium titanate and introduce a conjecture regarding the nature of the predominant defect in strontium-poor stoichiometries in samples grown via pulsed laser deposition. Finally, during the review process, we learned of recent experimental data, from strontium titanate films deposited via molecular-beam epitaxy, that show good agreement with our calculated value of the chemical strain associated with strontium vacancies.Comment: 14 pages, 11 figures, 4 table

Improving Patient Pre-screening for Clinical Trials: Assisting Physicians with Large Language Models

Physicians considering clinical trials for their patients are met with the laborious process of checking many text based eligibility criteria. Large Language Models (LLMs) have shown to perform well for clinical information extraction and clinical reasoning, including medical tests, but not yet in real-world scenarios. This paper investigates the use of InstructGPT to assist physicians in determining eligibility for clinical trials based on a patient's summarised medical profile. Using a prompting strategy combining one-shot, selection-inference and chain-of-thought techniques, we investigate the performance of LLMs on 10 synthetically created patient profiles. Performance is evaluated at four levels: ability to identify screenable eligibility criteria from a trial given a medical profile; ability to classify for each individual criterion whether the patient qualifies; the overall classification whether a patient is eligible for a clinical trial and the percentage of criteria to be screened by physician. We evaluated against 146 clinical trials and a total of 4,135 eligibility criteria. The LLM was able to correctly identify the screenability of 72% (2,994/4,135) of the criteria. Additionally, 72% (341/471) of the screenable criteria were evaluated correctly. The resulting trial level classification as eligible or ineligible resulted in a recall of 0.5. By leveraging LLMs with a physician-in-the-loop, a recall of 1.0 and precision of 0.71 on clinical trial level can be achieved while reducing the amount of criteria to be checked by an estimated 90%. LLMs can be used to assist physicians with pre-screening of patients for clinical trials. By forcing instruction-tuned LLMs to produce chain-of-thought responses, the reasoning can be made transparent to and the decision process becomes amenable by physicians, thereby making such a system feasible for use in real-world scenarios.Comment: 11 pages, 4 tables, 2 figure

Introducing Online Vitriol

In ‘How One Stupid Tweet Blew Up Justine Sacco’s Life’ (New York Times Magazine, 12 February 2015) Welsh journalist Jon Ronson investigated the effect on victims of public shaming through social media platforms and compared it to the history of public shaming as a form of punishment. Such punishments (the stocks, the pillory, the whipping pole) have gone out of practice, in part because they were considered too humiliating and socially annihilating for the person undergoing the punishment. Ronson finds a clear parallel in the effects of online public shaming in the victims of the present. [...

Joint multi-contrast Variational Network reconstruction (jVN) with application to rapid 2D and 3D imaging

Purpose: To improve the image quality of highly accelerated multi-channel MRI data by learning a joint variational network that reconstructs multiple clinical contrasts jointly. Methods: Data from our multi-contrast acquisition was embedded into the variational network architecture where shared anatomical information is exchanged by mixing the input contrasts. Complementary k-space sampling across imaging contrasts and Bunch-Phase/Wave-Encoding were used for data acquisition to improve the reconstruction at high accelerations. At 3T, our joint variational network approach across T1w, T2w and T2-FLAIR-weighted brain scans was tested for retrospective under-sampling at R=6 (2D) and R=4x4 (3D) acceleration. Prospective acceleration was also performed for 3D data where the combined acquisition time for whole brain coverage at 1 mm isotropic resolution across three contrasts was less than three minutes. Results: Across all test datasets, our joint multi-contrast network better preserved fine anatomical details with reduced image-blurring when compared to the corresponding single-contrast reconstructions. Improvement in image quality was also obtained through complementary k-space sampling and Bunch-Phase/Wave-Encoding where the synergistic combination yielded the overall best performance as evidenced by exemplarily slices and quantitative error metrics. Conclusion: By leveraging shared anatomical structures across the jointly reconstructed scans, our joint multi-contrast approach learnt more efficient regularizers which helped to retain natural image appearance and avoid over-smoothing. When synergistically combined with advanced encoding techniques, the performance was further improved, enabling up to R=16-fold acceleration with good image quality. This should help pave the way to very rapid high-resolution brain exams

Infertility - causes, diagnosis, preventive measures and methods of treatment

The problem of infertility affects approximately 20% of married couples, and the number of people affected by this problem is still increasing[5,6]. Developed countries are characterized by the prevalence of primary infertility, while in developing countries there is a high rate of secondary infertility[8,9]. The most common cause of marital infertility is obstruction of the fallopian tubes, which occurs in 30-35% of women and requires surgical intervention. However, both sexes are dominated by immunological and hormonal disorders (25%-30% of cases)[3,4]. The basic examination in which male fertility is determined is the semen analysis, while in women, many tests should be performed in order to make a diagnosis: anamnesis, gynecological examination, ultrasound performed repeatedly during the menstrual cycle (ovulation assessment), hormonal and immunological tests, post-coital tests, bacteriological cultures, hysterosalpingography or laparoscopy [20]. In vitro fertilization is the most effective of all methods of infertility treatment. In vitro fertilization can be performed using the classical method by adding prepared sperm to the egg cells or by microinjection of the sperm into the egg cell[21]