Perovskites Tilley, Richard J. D
2016, 2016-03-03, 2016-03-15
eBook
Uniquely describes both the crystallography and properties of perovskite related materials. * Practical applications in solar cells, microelectronics and telecommunications * Interdisciplinary topic ...drawing on materials science, chemistry, physics, and geology * Contains problems and answers to enhance knowledge retention
This paper studies a large-scale educational expansion to assess whether shocks to educational inputs affect the academic achievement of adult education students. I analyze the effects of a Swedish ...program that rapidly doubled enrollment in adult education, thus straining school resources. The program targeted low-educated, unemployed adults aged 25 and older. Therefore, my analysis focuses on students under age 25 to reduce the risk that changes in the characteristics of the study sample drive my findings. First, I show that students in regions subject to stronger enrollment expansions experienced stronger negative shocks to educational inputs, including teacher credentials, per-pupil expenditure, and peer quality. Second, I show that the stronger negative shocks to these inputs coincided with larger increases in course dropout. Taken together, the two sets of results suggest a causal link between educational inputs and students’ academic progress in adult education.
•I study a policy that rapidly expanded secondary-level adult education in Sweden.•The expansion negatively affected educational inputs, such as teacher credentials.•The declines in educational inputs coincided with increases in course dropout.•Shocks to educational inputs thus affect the academic progress of adult learners.
•The pandemic decreased students’ demand for service-related vocational programs in high school.•The decrease is most pronounced for programs related to the Accommodation and Food Services ...sector.•This sector was hardest hit, implying that labor market conditions affect students’ choices.•We find no change in demand for academic programs.
We study whether the onset of the COVID-19 crisis affected the program choices of high school applicants in Sweden. Our analysis exploits the fact that the admission process consists of two stages: a preliminary round in which applicants initially rank programs in order of preference and a final round in which they can alter their preliminary rankings. In 2020, the timing of the two rounds happened to provide a unique pre- and post-crisis snapshot of applicants’ field-of-study choices. Using school-level data on applicants’ top-ranked programs for all admission rounds between 2016 and 2020, we implement a difference-in-differences method to identify the immediate effect of the crisis on demand for programs. We find no change in demand for academic programs, but a decline in top-ranked applications to some of the vocational programs. The declines are most pronounced and robust for programs related to the Accommodation and Food Services sector, which was the most adversely affected industry during the crisis. This finding suggests that labor market considerations influence the study choices made by relatively young students.
We compare the singlet fission dynamics of five pentacene derivatives precipitated to form nanoparticles. Two nanoparticle types were distinguished by differences in their solid-state order and ...kinetics of triplet formation. Nanoparticles that comprise primarily weakly coupled chromophores lack the bulk structural order of the single crystal and exhibit nonexponential triplet formation kinetics (Type I), while nanoparticles that comprise primarily more strongly coupled chromophores exhibit order resembling that of the bulk crystal and triplet formation kinetics associated with the intrinsic singlet fission rates (Type II). In the highly ordered nanoparticles, singlet fission occurs most rapidly. We relate the molecular packing arrangement derived from the crystal structure of the pentacene derivatives to their singlet fission dynamics and find that slip stacking leads to rapid, subpicosecond singlet fission. We present evidence that exciton delocalization, coincident with an increased relative admixture of charge-transfer configurations in the description of the exciton wave function, facilitates rapid triplet pair formation in the case of single-step singlet fission. We extend the study to include two hexacene derivatives and find that these conclusions are generally applicable. This work highlights acene derivatives as versatile singlet fission chromophores and shows how chemical functionalization affects both solid-state order and exciton interactions and how these attributes in turn affect the rate of singlet fission.
The bacterial toxin pneumolysin is released as a soluble monomer that kills target cells by assembling into large oligomeric rings and forming pores in cholesterol-containing membranes. Using cryo-EM ...and image processing, we have determined the structures of membrane-surface bound (prepore) and inserted-pore oligomer forms, providing a direct observation of the conformational transition into the pore form of a cholesterol-dependent cytolysin. In the pore structure, the domains of the monomer separate and double over into an arch, forming a wall sealing the bilayer around the pore. This transformation is accomplished by substantial refolding of two of the four protein domains along with deformation of the membrane. Extension of protein density into the bilayer supports earlier predictions that the protein inserts β hairpins into the membrane. With an oligomer size of up to 44 subunits in the pore, this assembly creates a transmembrane channel 260 Å in diameter lined by 176 β strands.
Biologically derived organic molecules are a cost‐effective and environmentally benign alternative to the widely used metal‐based electrodes employed in current energy storage technologies. Here, the ...first bio‐derived pendant polymer cathode for lithium‐ion batteries is reported. The redox moiety is flavin and is derived from riboflavin (vitamin B2). A semi‐synthetic methodology is used to prepare the pendant polymer, which is composed of a poly(norbornene) backbone and pendant flavin units. This semi‐synthetic approach reduces the number of chemical transformations required to form this new functional material. Lithium‐ion batteries incorporating this polymer have a 125 mAh g−1 capacity and an ≈2.5 V operating potential. It is found that charge transport is greatly improved by forming hierarchical structures of the polymer with carbon black, and new insight into electrode degradation mechanisms is provided which should be applicable to polymer electrodes in general. This work provides a foundation for the use of bio‐derived pendant polymers in sustainable, high‐performance lithium‐ion batteries.
A pendant polymer with bio‐derived redox units is designed for lithium‐ion battery cathodes. With a working voltage of ≈2.5 V versus Li/Li+, it can deliver a high capacity of 125 mAh g−1 at 14.4 mA g−1. Using a semi‐synthetic approach for designing pendant redox‐active polymers is an attractive strategy for the development of energy storage materials.
Perylene diimides (PDIs) are one of the most widely studied n‐type materials, showing great promise as electron acceptors in organic photovoltaic devices and as electron transport materials in ...n‐channel organic field effect transistors. Amongst the well‐established chemical modification strategies for increasing the electron mobility of PDI, substitution of the imide oxygen atoms with sulfur, known as thionation, has remained largely unexplored. In this work, it is demonstrated that thionation is a highly effective means of enhancing the electron mobility of a bis‐N‐alkylated PDI derivative. Successive oxygen–sulfur substitution increases the electron mobility such that the fully thionated derivative (S4) has an average mobility of 0.16 cm2 V−1 s−1. This is two orders of magnitude larger than the nonthionated parent compound (P), and is achieved by solution deposition and without thermal or solvent vapor annealing. A combination of atomic force microscopy and 2D wide angle X‐ray scattering experiments, together with theoretical modeling of charge transport efficiency, is used to explain the strong positive correlation observed between electron mobility and degree of thionation. This work establishes thionation as a highly effective means of enhancing the electron mobility of PDI, and provides motivation for the development of thionated PDI derivatives for organic electronics applications.
The effect of oxygen–sulfur atomic substitution (thionation) on the electron mobility of perylene diimide is investigated. Electron mobility correlates with the extent of thionation, with the highest mobilities obtained in solution processed nonannealed devices. This work shows that thionation is a promising strategy for boosting the electron mobility of perylene diimide derivatives.
Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to ...considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet-triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields.
Sexual function of women can be affected by many factors resulting in female sexual dysfunction (FSD). Sexual dysfunction is a common problem among women of all ages and has negative effects not only ...on their quality of lives but also on the sexual function and quality of life of their partners. It can also affect mental health of the entire family and society. Regarding the multidimensional nature of female sexual dysfunction and considering its consequences, this condition needs to be recognised in its early stages in order to prevent future consequences and impacts. This article discusses biopsychosocial aspect of female sexual function, classifications and risk factors of female sexual dysfunction and investigates current approaches to identify and treat this problem.
The prevalence of mental health problems have been found to be higher among university students compared to their non-student peers. Nursing students in particular face a range of additional ...stressors which may impact their undergraduate performance and their careers. Mental Health First Aid (MHFA) aims to increase mental health literacy and to reduce stigma and may positively impact on the student population. This paper describes a MHFA randomised controlled trial targeting nursing students at a large Australian university. This study aimed to measure the impact of the MHFA course on mental health literacy, mental health first aid intentions, confidence in helping someone with a mental health problem and stigmatising attitudes including social distance.
Participants were first year nursing students (n = 181) randomly allocated to the intervention (n = 92) or control (n = 89) group. Intervention group participants received the standardised MHFA course for nursing students. Online self-report questionnaires were completed at three time intervals: baseline (one week prior to the intervention: T
) (n = 140), post intervention (T
) (n = 120), and two months post intervention (T
) (n = 109). Measures included demographics, mental health knowledge, recognition of depression, confidence in helping, mental health first aid intentions and stigmatising attitudes including social distance. Repeated measures ANOVA was computed to measure if the impact of time (T
, T
, T
) and group (intervention and control) on the outcome variables.
There was a significant improvement among intervention compared to control group participants across the three time periods for knowledge scores (p < 0.001), confidence in helping (p < 0.001), mental health first aid intentions (p < 0.001), total personal stigma (p < 0.05), personal dangerous/unpredictable stigma (p < 0.05) and social distance (p < 0.05) scores.
MHFA is useful training to embed in university courses and has the potential to enhance mental health literacy and reduce stigmatising attitudes and social distance. While this course has particular salience for nursing and other health science students, there are broader benefits to the general university population that should be considered and opportunities accordingly explored for all students to complete the course.
Australian New Zealand Clinical Trials Registry ACTRN12614000861651 . Retrospectively registered 11 August 2014.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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