The Impact of McCarthyism on the African American Freedom Movement, Revisited

This collection of essays edited by U.S. historians Robbie Lieberman and Clarence Lang is an important contribution to the growing field of ‘revisionist’ historiography, which deals with 1950s U.S. culture and a renewed understanding of the early Cold War, anticommunism and its relation to the African American fight for racial progress. The six essays focusing on little-known aspects of 1950s black radical activism argue for the destructive impact which McCarthyism had on the African American movement for racial equality. They thereby ultimately challenge and complicate the historiographical notion that the Cold War was beneficial to the success of the black freedom movement

Investigating the role of micro RNAs in retinal development and as agents of degeneration

Micro RNAs (miRNAs) are potent post-transcriptional regulators of gene expression, which play a myriad of roles throughout human development and are key regulators of retinal development, as well as being implicated in retinal disease. The exact roles played by miRNAs in these processes are imperfectly understood. The miR-182, 96, 183 Sensory Cluster is a sensory organ-specific miRNA family and the most highly expressed miRNA family in the murine retina, yet the developmental roles it plays remain unclear. Whilst miRNA dysregulation is associated with certain retinopathies, whether dysregulation is a disease marker or plays a causative role in photoreceptor death, is unknown. This thesis investigated miRNA expression and function in human retinal development and the genetic retinopathy Type I Usher syndrome. Human pluripotent stem cell-derived retinal organoids provided a human tissue model for this study. A CRISPR-Cas9 gene editing platform was applied to modify the genome in hPSCs and investigate the effect on organoid development; Sensory Cluster knockout hESC lines and both patient and isogenic control TypeI Usher patient-derived iPSC lines were generated and analysed. Sensory Cluster function was interrogated using a gain and loss-of-function approach; over expression by miRNA mimic treatment was shown to lead to an increase in expression of certain photoreceptor maturation markers; Sensory Cluster knockout organoids were analysed using morphological and transcriptomic analyses. The molecular phenotype of Type I Usher in vitro was also interrogated using RNAseq. Type I Usher patient organoids displayed reduced expression of photoreceptor-associated genes, including the Sensory Cluster, but these findings were not recapitulated in organoids generated from a wider panel of Type I hPSC lines. These studies provide insight into the role of the Sensory Cluster in the human retina and the value of gene edited hPSCs to analyse human gene function. It also highlighted the heterogeneity between organoid differentiations and hPSC lines

Unification of Nonlinear Anomalous Hall Effect and Nonreciprocal Magnetoresistance in Metals by the Quantum Geometry

The quantum geometry has significant consequences in determining transport and optical properties in quantum materials. Here, we use a semiclassical formalism coupled with perturbative corrections unifying the nonlinear anomalous Hall effect (NLAHE) and nonreciprocal magnetoresistance (NMR, longitudinal resistance) from the quantum geometry. In the dc limit, both transverse and longitudinal nonlinear conductivities include a term due to the normalized quantum metric dipole. The quantum metric contribution is intrinsic and does not scale with the quasiparticle lifetime. We demonstrate the coexistence of a NLAHE and NMR in films of the doped antiferromagentic topological insulator MnBi$_2$Te$_4$. Our work indicates that both longitudinal and transverse nonlinear transport provide a sensitive probe of the quantum geometry in solids.Comment: 4.5 pages; 2 figures. SI. Comments welcome

General nonlinear Hall current in magnetic insulators beyond the quantum anomalous Hall effect

Can a generic magnetic insulator exhibit a Hall current? The quantum anomalous Hall effect (QAHE) is one example of an insulating bulk carrying a quantized Hall conductivity and other insulators (with zero Chern number) present zero Hall conductance in the linear response regime. Here, we find that a general magnetic insulator possesses a nonlinear Hall conductivity quadratic to the electric field if the system breaks inversion symmetry. This conductivity originates from an induced orbital magnetization due to virtual interband transitions. We identify three contributions to the wavepacket motion, a velocity shift, a positional shift, and a Berry curvature renormalization. In contrast to the crystalline solid, we find that this nonlinear Hall conductivity vanishes for Landau levels of a 2D electron gas, indicating a fundamental difference between the QAHE and the Integer quantum Hall effect