Scattering and Pairing in Cuprate Superconductors

The origin of the exceptionally strong superconductivity of cuprates remains a subject of debate after more than two decades of investigation. Here we follow a new lead: The onset temperature for superconductivity scales with the strength of the anomalous normal-state scattering that makes the resistivity linear in temperature. The same correlation between linear resistivity and Tc is found in organic superconductors, for which pairing is known to come from fluctuations of a nearby antiferromagnetic phase, and in pnictide superconductors, for which an antiferromagnetic scenario is also likely. In the cuprates, the question is whether the pseudogap phase plays the corresponding role, with its fluctuations responsible for pairing and scattering. We review recent studies that shed light on this phase - its boundary, its quantum critical point, and its broken symmetries. The emerging picture is that of a phase with spin-density-wave order and fluctuations, in broad analogy with organic, pnictide, and heavy-fermion superconductors.Comment: To appear in Volume 1 of the Annual Review of Condensed Matter Physic

Genetic Variation of the DGAT1 gene in Dual-Purpose Dairy Cows and its Influence on Economically Important Breeding Traits

BackgroundOver the last 10 years, the discovery of individual, or candidate, genes that influence economically important traits has revolutionised how the dairy industry selects cows for breeding programmes. One such gene, the diacylglycerol O-acyltransferase 1 (DGAT1) gene is significant in dairy production as it is associated with the synthesis of fat in milk, and polymorphisms within the gene can be used for selection purposes. In this study, the variants (genotypes) of the K232A polymorphism of the DGAT1 gene, within a dual-purpose dairy herd, bred for both dairy and beef production, were determined, and compared to the Economic Breeding Index (EBI) and EBI sub-indexes to ascertain if any statistically significant relationships existed. MethodsDNA was extracted from hair samples, and the genotypes of the DGAT1 gene were determined using a combination of conventional PCR, restriction fragment length polymorphism (RFLP), gel electrophoresis, DNA sequencing and novel real-time PCR assays. ResultsThe three genotypes within the herd were: KK (n = 5), AA (n = 10), KA (n = 8). KK denoted a homologous Lysine allele, AA denoted a homologous Alanine allele, and KA denoted a heterologous Lysine allele. There was no association found between the milk production traits and the DGAT1 K232A genotype (P = 0.178). However, there was a significant association found between the K232A polymorphism and other EBI traits including ‘Beef’ and ‘Management’ which had P values of 0.035 and 0.023 respectively. The AA genotype was associated with higher beef traits (higher carcass values) and lower management traits (reduced milking time and good temperament). The KK genotype was associated with higher management traits and lower beef traits. These results were not always consistent with those in the literature. ConclusionsThis study showed that animals with the A allele of the DGAT1 gene polymorphism may be better suited for dual-purpose dairy herds. It is also possible that different breeding goals and farm environments may influence the results suggesting that these types of studies should be conducted on a variety of herds and include larger samples sizes

Genotype and diet affect resistance, survival, and fecundity but not fecundity tolerance

Insects are exposed to a variety of potential pathogens in their environment, many of which can severely impact fitness and health. Consequently, hosts have evolved resistance and tolerance strategies to suppress or cope with infections. Hosts utilizing resistance improve fitness by clearing or reducing pathogen loads, and hosts utilizing tolerance reduce harmful fitness effects per pathogen load. To understand variation in, and selective pressures on, resistance and tolerance, we asked to what degree they are shaped by host genetic background, whether plasticity in these responses depends upon dietary environment, and whether there are interactions between these two factors. Females from ten wild‐type Drosophila melanogaster genotypes were kept on high‐ or low‐protein (yeast) diets and infected with one of two opportunistic bacterial pathogens, Lactococcus lactis or Pseudomonas entomophila. We measured host resistance as the inverse of bacterial load in the early infection phase. The relationship (slope) between fly fecundity and individual‐level bacteria load provided our fecundity tolerance measure. Genotype and dietary yeast determined host fecundity and strongly affected survival after infection with pathogenic P. entomophila. There was considerable genetic variation in host resistance, a commonly found phenomenon resulting from for example varying resistance costs or frequency‐dependent selection. Despite this variation and the reproductive cost of higher P. entomophila loads, fecundity tolerance did not vary across genotypes. The absence of genetic variation in tolerance may suggest that at this early infection stage, fecundity tolerance is fixed or that any evolved tolerance mechanisms are not expressed under these infection conditions

A hierarchy of bound states in the 1D ferromagnetic Ising chain CoNb2_2O6_6 investigated by high resolution time-domain terahertz spectroscopy

Kink bound states in the one dimensional ferromagnetic Ising chain compound CoNb$_2$O$_6$ have been studied using high resolution time-domain terahertz spectroscopy in zero applied magnetic field. When magnetic order develops at low temperature, nine bound states of kinks become visible. Their energies can be modeled exceedingly well by the Airy function solutions to a 1D Schr\"odinger equation with a linear confining potential. This sequence of bound states terminates at a threshold energy near two times the energy of the lowest bound state. Above this energy scale we observe a broad feature consistent with the onset of the two particle continuum. At energies just below this threshold we observe a prominent excitation that we interpret as a novel bound state of bound states -- two pairs of kinks on neighboring chains

“Difficult but worth it”: Exploring the Experiences of Women in Engineering during Co-op

Despite an extensive amount of research focusing on women in engineering, the gender disparity within the engineering workforce is the most significant amongst workforce disparities in the United States (National Science Foundation, 2018), with engineering being labeled the “last gender-equitable profession” (Pierrakos, Beam, Constantz, Johri, & Anderson, 2009, M4F-1). Although there is a substantial amount of literature on the experience of women in engineering, there has been little progress in regard to the recruitment and retention of women engineers in higher education and in the workforce over the past several decades. The current study implements a Participatory Action Research framework to better understand women engineering students’ experiences participating in cooperative education (co-op), with the goal to explore their experiences through a participatory process and support their development of action items. We employed a qualitative participatory method, Group Level Assessment (GLA), to explore the women\u27s experiences on co-op. The GLA method allowed for the women participants to be involved with the data generation, data analysis, and prioritization. Action items developed by participants would then be shared with appropriate stakeholders, such as Deans, administrators, and employer- in hopes of creating positive change. Themes were developed by participants through discussion during the GLAs. Themes include, (1) impact of relationships, (2) struggle for equality, and (3) growth through the co-op experience. In addition to the description of the themes, narratives accompany each of the themes, designed to illustrate the thematic ideas, topics, and tensions. The themes we discovered had significant overlap and crossover, helping to reiterate the complexity and uniqueness of each woman\u27s experience. The women agreed that co-op was an opportunity to learn, grow professionally, and gain exposure in their field of study, however, many women find it difficult to navigate the experience. Several of the women noted not feeling heard or seen during their co-op experience, recognizing they were highly visible as women but not as engineers. The ability to connect and feel supported while on co-op contributed to women’s confidence and influenced their overall growth during the experience, giving them a sense of belonging. Our study found that relationships are the key contributor to women’s learning, growth, and development during the co-op experience. This is a significant finding, acknowledging that if women are at a disadvantage in the growth and learning process during co-op, due to the contextual factors associated with building relationships, this will ultimately hamper their ability to contribute in the future and progress in the field. It can be hypothesized that until women have equal access to developing relationships with peers, colleagues, and supervisors, they will continue to be at a disadvantage in the engineering space