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Environmental stability remains a major challenge for the commercialisation of organic solar cells and degradation pathways remain poorly understood. Designing materials for improved device stability requires an understanding of the relationship between the properties of the donor or acceptor molecule and different degradation mechanisms. Here we study the correlations between various molecular parameters of the fullerene derivative bis-PCBM and the degradation rate of polymer:bis-PCBM organic solar cells, based on the same carbazole-alt-benzothiadiazole polymer, in aerobic and anaerobic conditions. We compare eight high purity bis-PCBM isomers with different electronic, chemical and packing properties along with PCBM and the mixture of bis isomers. In the case of aerobic photodegradation, we find that device degradation rate is positively correlated to the LUMO energy of the bis-PCBM isomer and to the degree of crystallinity of the isomer, while the correlation of degradation with driving force for epoxide formation is unclear. These results support the idea that in these samples, aerobic photodegradation proceeds via superoxide formation by the photogenerated polaron on the fullerene, followed by further chemical reaction. In the absence of air, photodegradation rate is correlated with molecular structure, supporting the mechanism of microstructural degradation via fullerene dimerization. The approach and findings presented here show how control of specific molecular parameters through chemical design can serve as a strategy to enhance stability of organic solar cells.

While a number of studies in recent years explore the particularistic tendencies of presidents – targeting various benefits to districts and states that will help their and their party’s electoral prospects – little work has explored how members of Congress react to such behavior. We take some initial steps in this regard by examining how members have responded to President Donald Trump’s trade initiatives. We analyze congressional newsletter mentions of tariffs or trade as a means of exploring congressional reaction. We find a positive relationship between tariff/trade mentions and partisanship, as Republican members and members from states that Trump won in 2016 are more likely to refer to tariffs/trade in their newsletters. This represents, we argue, a different kind of credit claiming. These basic empirical patterns set the stage for more systematic analysis in the future.

Environmental stability remains a major challenge for the commercialisation of organic solar cells and degradation pathways remain poorly understood. Designing materials for improved device stability requires an understanding of the relationship between the properties of the donor or acceptor molecule and different degradation mechanisms. Here we study the correlations between various molecular parameters of the fullerene derivative bis-PCBM and the degradation rate of polymer:bis-PCBM organic solar cells, based on the same carbazole

The development of non-fullerene acceptors (NFAs) has facilitated the realization of efficient organic solar cells (OSCs) with minimal burn-in losses and excellent long-term stability. However, the role of NFA molecular structures on device stability remains unclear, limiting commercialization of NFA-based OSCs. Herein, the photostability of 10 OSC devices, fabricated with various NFAs (O-IDTBR, EH-IDTBR, ITIC, and ITIC-M) blended with donor polymers (PTB7-Th, PffBT4T-2OD, and PBDB-T), is investigated. O-IDTBR and EH-IDTBR form highly stable devices with all three polymers, whereas ITIC and ITIC-M devices suffer from burn-in losses and long-term degradation. Conformational instability is found to be responsible for the poor photostability of ITIC and ITIC-M, resulting in poor device stability. Twisting and potential breakage of the chemical bond that links the end group to the main backbone of ITIC and ITIC-M molecules causes undesirable conformational changes. Potential strategies to overcome such detrimental photo-induced conformational changes in NFAs are proposed. Funding Agencies|European Social Fund via the Welsh Government; EPSRCUK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) [EP/L015099/1, EP/T026219/1, EP/S020748/1]; UK EPSRCUK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) [EP/L016702/1]; ATIP Programme grant [EP/T028513/1]; CSEM Brasil; Global Research Laboratory Program of the National Research Foundation (NRF) - Ministry of Science, ICT & Future Planning [NRF-2017K1A1A2013153]; UKRI Global Challenge Research Fund project, SUNRISE [EP/P032591/1]; Office of Sponsored Research (OSR) [OSR-2018-CRG/CCF-3079, OSR-2019-CRG8-4086, OSR-2018-CRG7-3749]; European Social Fund, European Union CSEM Brasil, Brazil European Research Council, European Union ERC Synergy Grant [SC2 (610115)]; European Unions Horizon 2020 research and innovation programme [952911]; project BOOSTER [862474]; project RoLA-FLEX; KAUSTKing Abdullah University of Science & Technology

Early American political leaders were tasked with sustaining a representative republic on a seemingly impossible scale. Their struggle to stave off political dissolution raises an important question for scholars of federalism. How can democratic governments integrate disparate political communities across a vast—and rapidly expanding—territory? We revisit the solution most often proposed by contemporary political leaders: a nationally directed system of internal improvements. Using a dataset of nineteenth-century appropriations, we find that patterns in internal improvement funding are consistent with a nation-building strategy. Congressional districts at the fringes of the republic received disproportionate support from the federal government, even after accounting for political preferences, positions of legislative authority, and sub-national spending patterns. Our research stands in contrast to existing work on internal improvements, which is primarily interested in testing theories of distributive politics, and contributes to a diverse body of research on federalism, nation-building, congressional politics, and American political development.

Instructors routinely and reasonably express frustration when students choose not to complete required reading assignments. Readings are chosen because they are important, and the decision to not e...

I analyse the relative influence of lawmakers before and after a watershed moment in the development of faction institutions: the abolition of legislative service organizations. Blocs of lawmakers in the House of Representatives were afforded official resources to advance their policy agendas between 1979 and 1995. In the wake of the “Republican Revolution,” however, these groups were categorically dismantled. Using a difference-in-difference design, I estimate the individual-level effect of losing congressional resources on relative legislative effectiveness. The results inform our understanding of faction power, legislative bargaining and evolving congressional institutions.

We develop a subjective measure of candidate ideology in political communication, based on human coders evaluations of ideological position-taking in campaign advertisements. Our dynamic measure al...

We review attempts to evaluate Pivotal Politics and related theories in light of the social sciences’ movement toward causal empiricism. To accommodate limitations of available data, most existing ...

We conduct a preliminary analysis of the first 200 days of the Donald Trump presidency, to determine who his principal allies in the US House have been. We build our analysis around three groups of Republicans, based on caucus affiliations: members of the Republican Main Street Partnership (RMSP), the Republican Study Committee (RSC), and the House Freedom Caucus (HFC). We find that House Republicans, regardless off caucus membership, broadly support President Trump and largely shared in the his electoral success. Yet, we also uncover suggestive evidence that the HFC is maneuvering into a position of influence with President Trump. Freedom Caucus members are more closely tied to his electoral performance than members of other conservative groups, and they appear to receive more time with the President relative to a comparable group of House Republicans. While these results are interesting, they are also initial and more time is needed to assess how President Trump builds a winning coalition with Republican House members.

Research on presidential distributive politics focuses almost exclusively on federal domestic spending. Yet, presidential influence on public policy extends well-beyond grant allocation. Since the early 20th Century, for example, the president has had substantial discretion to adjust tariff schedules and non-tariff barriers “with the stroke of a pen.” These trade adjustments via presidential directive allow us to test the logic of presidential particularism in an area of policy understudied among presidency scholars. We examine unilateral adjustments to US trade policies between 1917 and 2006, with a detailed analysis of those made between 1986 and 2006, and find that presidents—in accordance with electoral incentives—strategically allocate trade protections to industries in politically valuable states. In general, states in which the president lacks a comfortable electoral majority are systematically more likely to receive protectionist unilateral orders. Overall, our results show that the president’s distributive imperative extends into the realm of foreign affairs, an arena in which the president has substantial authority to influence public policy.

The recent emergence of non-fullerene small molecule acceptors has reinvigorated the field of organic solar cells, already resulting in significant breakthroughs in their power conversion efficiency and discovery of remarkable new science. The stability and degradation of this class of materials and devices, on the other hand, has to date received relatively less attention. Herein, we present a critical review into the fundamentally different degradation mechanisms of non-fullerene acceptors compared to fullerene acceptors, as well as the very different roles they play upon the charge carrier generation and recombination kinetics and the resulting solar cell stability. We highlight in particular the prospect of the emergence of non-fullerene acceptors in addressing several major degradation mechanisms related to the use of fullerene acceptors, in conjunction with a number of unique degradation mechanisms that only exist in non-fullerene acceptors, which would provide an important guideline for further developments toward achieving long-term stability of organic solar cells.

With the emergence of nonfullerene electron acceptors resulting in further breakthroughs in the performance of organic solar cells, there is now an urgent need to understand their degradation mechanisms in order to improve their intrinsic stability through better material design. In this study, we present quantitative evidence for a common root cause of light-induced degradation of polymer:nonfullerene and polymer:fullerene organic solar cells in air, namely, a fast photo-oxidation process of the photoactive materials mediated by the formation of superoxide radical ions, whose yield is found to be strongly controlled by the lowest unoccupied molecular orbital (LUMO) levels of the electron acceptors used. Our results elucidate the general relevance of this degradation mechanism to both polymer:fullerene and polymer:nonfullerene blends and highlight the necessity of designing electron acceptor materials with sufficient electron affinities to overcome this challenge, thereby paving the way toward achieving long-term solar cell stability with minimal device encapsulation.

Much of the literature on partisan agenda setting in Congress focuses on the majority’s ability to exercise negative agenda control. As a result, the empirical emphasis has been on “rolls,” or how often the majority of the majority party opposes legislation that nonetheless passes. Although interesting, rolls are only one source of majority party failure. The other source, largely unexplored in the literature, is when the majority of the majority party supports legislation that is subsequently defeated. These cases represent “disappointments,” and are a means to determine how effective the majority party is at exercising positive agenda control. Making some basic modifications to a standard spatial model of agenda setting, we articulate why and where we might expect the majority party to fail to exercise positive agenda control effectively. We then derive hypotheses regarding (1) which members should vote “no” on roll calls that result in a disappointment and (2) why disappointments vary on a Congress-by-Congress basis across time, and test them using a dataset of final-passage votes on House bills in the post-Reconstruction era.

While a number of studies have examined the politics of tariff decision-making in the United States, little work has examined the subsequent political effects of tariff policy. We help fill this gap in the literature by analyzing—both theoretically and empirically—the electoral implications of tariff revision. Specifically, we investigate the veracity of the Cannon Thesis—the proposition advanced by Speaker Joe Cannon in 1910 that the majority party in the U.S. House was punished when it made major revisions to the tariff. We find that from 1877 to 1934 major tariff revisions were, on average, associated with a significant loss of votes for majority-party members—both regionally and nationally—that translated into a loss of House seats. We find support for the notion that major tariff revisions generated inordinate uncertainty among various business interests, which the opposition party could then use (by leveraging fear and market instability) to mobilize its base and gain ground in the following election. Our results provide a new explanation for the delegation of tariff policymaking to the executive branch.

Though considerable research focuses on formal institutions in Congress, scholars have long acknowledged that much of what guides legislative behavior is unwritten. To advance this area, we leverage a tool that allows appropriators to redirect billions of dollars from mandatory programs to discretionary projects. Changes in mandatory program spending—known as “CHIMPs”—show that existing institutions are often maintained by the strategic action of legislators. In the case of CHIMPs, we find their use is largely a response to formal constraints and that they are preserved through avoidance of minimum reform coalitions. This highlights that the legislative process—and budgetary outcomes in particular—cannot be understood without attention to procedures which remain “off the books.”

We compared the gastrointestinal effects of milk-based diets in which the β-casein component was either the A1 or A2 type in male Wistar rats fed the experimental diets for 36 or 84 h. Gastrointestinal transit time was significantly greater in the A1 group, as measured by titanium dioxide recovery in the last 24 h of feeding. Co-administration of naloxone decreased gastrointestinal transit time in the A1 diet group but not in the A2 diet group. Colonic myeloperoxidase and jejunal dipeptidyl peptidase (DPP)-4 activities were greater in the A1 group than in the A2 group. Naloxone attenuated the increase in myeloperoxidase activity but not that in DPP-4 activity in the A1 group. Naloxone did not affect myeloperoxidase activity or DPP-4 activity in the A2 group. These results confirm that A1 β-casein consumption has direct effects on gastrointestinal function via opioid-dependent (gastrointestinal transit and myeloperoxidase activity) and opioid-independent (DPP-4 activity) pathways.

SummaryThe antigen receptor for natural killer T cells (NKT TCR) binds CD1d-restricted microbial and self-lipid antigens, although the molecular basis of self-CD1d recognition is unclear. Here, we have characterized NKT TCR recognition of CD1d molecules loaded with natural self-antigens (Ags) and report the 2.3 Å resolution structure of an autoreactive NKT TCR-phosphatidylinositol-CD1d complex. NKT TCR recognition of self- and foreign antigens was underpinned by a similar mode of germline-encoded recognition of CD1d. However, NKT TCR autoreactivity is mediated by unique sequences within the non-germline-encoded CDR3β loop encoding for a hydrophobic motif that promotes self-association with CD1d. Accordingly, NKT cell autoreactivity may arise from the inherent affinity of the interaction between CD1d and the NKT TCR, resulting in the recognition of a broad range of CD1d-restricted self-antigens. This demonstrates that multiple self-antigens can be recognized in a similar manner by autoreactive NKT TCRs.

Post-translational modification of protein serines/threonines with N-acetylglucosamine (O-GlcNAc) is dynamic, inducible and abundant, regulating many cellular processes by interfering with protein phosphorylation. O-GlcNAcylation is regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase, both encoded by single, essential, genes in metazoan genomes. It is not understood how OGT recognises its sugar nucleotide donor and performs O-GlcNAc transfer onto proteins/peptides, and how the enzyme recognises specific cellular protein substrates. Here, we show, by X-ray crystallography and mutagenesis, that OGT adopts the (metal-independent) GT-B fold and binds a UDP-GlcNAc analogue at the bottom of a highly conserved putative peptide-binding groove, covered by a mobile loop. Strikingly, the tetratricopeptide repeats (TPRs) tightly interact with the active site to form a continuous 120 A putative interaction surface, whereas the previously predicted phosphatidylinositide-binding site locates to the opposite end of the catalytic domain. On the basis of the structure, we identify truncation/point mutants of the TPRs that have differential effects on activity towards proteins/peptides, giving first insights into how OGT may recognise its substrates.

Natural killer T cells (NKT cells) are divided into type I and type II subsets on the basis of differences in their T cell antigen receptor (TCR) repertoire and CD1d-antigen specificity. Although the mode by which type I NKT cell TCRs recognize CD1d-antigen has been established, how type II NKT cell TCRs engage CD1d-antigen is unknown. Here we provide a basis for how a type II NKT cell TCR, XV19, recognized CD1d-sulfatide. The XV19 TCR bound orthogonally above the A' pocket of CD1d, in contrast to the parallel docking of type I NKT cell TCRs over the F' pocket of CD1d. At the XV19 TCR-CD1d-sulfatide interface, the TCRα and TCRβ chains sat centrally on CD1d, where the malleable CDR3 loops dominated interactions with CD1d-sulfatide. Accordingly, we highlight the diverse mechanisms by which NKT cell TCRs can bind CD1d and account for the distinct antigen specificity of type II NKT cells.

The most potent foreign antigens for natural killer T cells (NKT cells) are α-linked glycolipids, whereas NKT cell self-reactivity involves weaker recognition of structurally distinct β-linked glycolipid antigens. Here we provide the mechanism for the autoreactivity of T cell antigen receptors (TCRs) on NKT cells to the mono- and tri-glycosylated β-linked agonists β-galactosylceramide (β-GalCer) and isoglobotrihexosylceramide (iGb3), respectively. In binding these disparate antigens, the NKT cell TCRs docked onto CD1d similarly, achieving this by flattening the conformation of the β-linked ligands regardless of the size of the glycosyl head group. Unexpectedly, the antigenicity of iGb3 was attributable to its terminal sugar group making compensatory interactions with CD1d. Thus, the NKT cell TCR molds the β-linked self ligands to resemble the conformation of foreign α-linked ligands, which shows that induced-fit molecular mimicry can underpin the self-reactivity of NKT cell TCRs to β-linked antigens.

Milk from dairy cows has long provided a high quality source of protein and selected micronutrients such as calcium to most populations. Recently, a relationship between disease risk and consumption of a specific bovine ss-casein fraction either A1 or A2 genetic variants has been identified. Populations, which consume milk containing high levels of ss-casein A2 variant, have a lower incidence of cardiovascular disease and type 1 diabetes. Furthermore, consumption of milk with the A2 variant may be associated with less severe symptoms of autism and schizophrenia. The mechanism of action focuses on ss-casein A1 and related forms preferentially that are able to produce a bioactive opioid peptide, ss-casomorphin-7 (ss-CM-7) during digestion. Infants may absorb ss-CM-7 due to an immature gastrointestinal tract. Adults, on the other hand, appear to reap the biological activity locally on the intestinal brush boarder. ss-CM-7 can potentially affect numerous opioid receptors in the nervous, endocrine, and immune systems. Whether there is a definite health benefit to milk containing the A2 genetic variant is unknown and requires further investigation.

This study aimed to identify genes or gene products associated with high lean muscle mass in bovines that may serve as potential markers for selection. An animal with a genetic predisposition to high lean muscle mass, the Belgium Blue, was chosen as a model to compare with the Holstein Friesian, a model that does not. Two-dimensional polyacrylamide gel electrophoresis analysis was utilized to compare the exhibited skeletal muscle proteome between the two animal types at two stages of foetal development. A previously uncharacterized polymorphism of a high expression myofibrillar protein, myosin light chain 1 fast (MLC-1f), was observed. The characterization of this polymorphism revealed a two amino acid insertion in a part of the protein that has been implicated in modulating myosin S1 ATPase activity. Furthermore, this polymorphism was shown to be the product of two alleles that are codominant. Screening studies were carried out on selected herds and showed a very high frequency of one allele. Both isoforms of MLC-1f were produced by recombinant means and purified. The recombinant proteins were exchanged into purified myosin hexamers that were then subject to assays measuring ATP consumption. The sensitivity of the assay utilized could not reveal any significant difference in ATPase activity between hexamers containing one or the other isoform.