Electronic properties of Fabre charge-transfer salts under various temperature and pressure conditions

Using density functional theory, we determine parameters of tight-binding Hamiltonians for a variety of Fabre charge transfer salts, focusing in particular on the effects of temperature and pressure. Besides relying on previously published crystal structures, we experimentally determine two new sets of structures; (TMTTF)$_2$SbF$_6$ at different temperatures and (TMTTF)$_2$PF$_6$ at various pressures. We find that a few trends in the electronic behavior can be connected to the complex phase diagram shown by these materials. Decreasing temperature and increasing pressure cause the systems to become more two-dimensional. We analyze the importance of correlations by considering an extended Hubbard model parameterized using Wannier orbital overlaps and show that while charge order is strongly activated by the inter-site Coulomb interaction, the magnetic order is only weakly enhanced. Both orders are suppressed when the effective pressure is increased.Comment: 12 pages, 16 figure

“Exploring the Basement of Social Justice Issues”: A Graduate Upon Graduation

Photograph of rides building up, taken J. Stevens' Fair, 20 June 1961 whole general view, looking West. See Leeson's notebook 9, pages 92-95 for notes

Multiferroic FeTe2_2O5_5Br: Alternating spin chains with frustrated interchain interactions

A combination of density functional theory calculations, many-body model considerations, magnetization and electron spin resonance measurements shows that the multiferroic FeTe$_2$O$_5$Br should be described as a system of alternating antiferromagnetic $S=5/2$ chains with strong Fe-O-Te-O-Fe bridges weakly coupled by two-dimensional frustrated interactions, rather than the previously reported tetramer models. The peculiar temperature dependence of the incommensurate magnetic vector can be explained in terms of interchain exchange striction being responsible for the emergent net electric polarization.Comment: 7 pages, 6 figure

Emergence of magnetism in graphene materials and nanostructures

Magnetic materials and nanostructures based on carbon offer unique opportunities for future technological applications such as spintronics. This article reviews graphene-derived systems in which magnetic correlations emerge as a result of reduced dimensions, disorder and other possible scenarios. In particular, zero-dimensional graphene nanofragments, one-dimensional graphene nanoribbons, and defect-induced magnetism in graphene and graphite are covered. Possible physical mechanisms of the emergence of magnetism in these systems are illustrated with the help of computational examples based on simple model Hamiltonians. In addition, this review covers spin transport properties, proposed designs of graphene-based spintronic devices, magnetic ordering at finite temperatures as well as the most recent experimental achievements.Comment: tutorial-style review article -- 18 pages, 19 figure

Abuse‐Related Post‐Traumatic Stress, Coping, and Tobacco Use in Pregnancy

Objective: To examine the relationship between trauma history, posttraumatic stress disorder (PTSD), coping, and smoking in a diverse sample of pregnant women, some of whom are active smokers. Design: Secondary analysis from a prospective study on PTSD and pregnancy outcomes. Setting: Maternity clinics at three health systems in the midwestern United States. Participants: Women age 18 or older (1,547) interviewed at gestational age fewer than 28 weeks. Methods: Participants were classified at nonsmokers, quitters (stopped smoking during pregnancy), and pregnancy smokers. Demographic, trauma, and pregnancy factors, substance use, and use of tobacco to cope were compared across groups. Logistic regression assessed the influence of these factors on being a smoker versus a nonsmoker and a quitter versus a pregnancy smoker. Results: Smokers differed from nonsmokers on all demographic risk factors (being African American, being pregnant as a teen, having lower income and less education, and living in high‐crime areas), had higher rates of current and lifetime PTSD, and were more likely to report abuse as their worst trauma. Pregnancy smokers had lower levels of education, were more likely to classify their worst trauma as “extremely troubling,” and were more likely to exhibit PTSD hyperarousal symptoms. In regression models, smoking “to cope with emotions and problems” doubled the odds of continuing to smoke while pregnant even after accounting for several relevant risk factors. Conclusion: Smoking behavior in pregnancy may be influenced by the need to cope with abuse‐related PTSD symptoms. Clinicians should consider using trauma‐informed interventions when working with tobacco‐using pregnant women.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86982/1/j.1552-6909.2011.01261.x.pd

Dcc Regulates Asymmetric Outgrowth of Forebrain Neurons in Zebrafish

The guidance receptor DCC (deleted in colorectal cancer) ortholog UNC-40 regulates neuronal asymmetry development in Caenorhabditis elegans, but it is not known whether DCC plays a role in the specification of neuronal polarity in vertebrates. To examine the roles of DCC in neuronal asymmetry regulation in vertebrates, we studied zebrafish anterior dorsal telencephalon (ADt) neuronal axons. We generated transgenic zebrafish animals expressing the photo-convertible fluorescent protein Kaede in ADt neurons and then photo-converted Kaede to label specifically the ADt neuron axons. We found that ADt axons normally project ventrally. Knock down of Dcc function by injecting antisense morpholino oligonucleotides caused the ADt neurons to project axons dorsally. To examine the axon projection pattern of individual ADt neurons, we labeled single ADt neurons using a forebrain-specific promoter to drive fluorescent protein expression. We found that individual ADt neurons projected axons dorsally or formed multiple processes after morpholino knock down of Dcc function. We further found that knock down of the Dcc ligand, Netrin1, also caused ADt neurons to project axons dorsally. Knockdown of Neogenin1, a guidance receptor closely related to Dcc, enhanced the formation of aberrant dorsal axons in embryos injected with Dcc morpholino. These experiments provide the first evidence that Dcc regulates polarized axon initiation and asymmetric outgrowth of forebrain neurons in vertebrates