Two-dimensional frustrated spin systems in high magnetic fields

We discuss our numerical results on the properties of the S = 1/2 frustrated J1-J2 Heisenberg model on a square lattice as a function of temperature and frustration angle phi = atan(J2/J1) in an applied magnetic field. We cover the full phase diagram of the model in the range -pi <= phi <= pi. The discussion includes the parameter dependence of the saturation field itself, and addresses the instabilities associated with it. We also discuss the magnetocaloric effect of the model and show how it can be used to uniquely determine the effective interaction constants of the compounds which were investigated experimentally.Comment: 4 pages, 5 figures, proceedings of RHMF 200

The double life of electrons in magnetic iron pnictides, as revealed by NMR

We present a phenomenological, two-fluid approach to understanding the magnetic excitations in Fe pnictides, in which a paramagnetic fluid with gapless, incoherent particle-hole excitations coexists with an antiferromagnetic fluid with gapped, coherent spin wave excitations. We show that this two-fluid phenomenology provides an excellent quantitative description of NMR data for magnetic "122" pnictides, and argue that it finds a natural justification in LSDA and spin density wave calculations. We further use this phenomenology to estimate the maximum renormalisation of the ordered moment that can follow from low-energy spin fluctuations in Fe pnictides. We find that this is too small to account for the discrepancy between ab intio calculations and neutron scattering measurements.Comment: Accepted for publication in Europhys. Lett. 6 pages, 4 figure

Domestic Violence, Employment and Divorce

Using unique, representative data on domestic violence, we document several stylized facts on abuse: the average characteristics of abused wives and abusive husbands are markedly different than the characteristics of individuals in non-violent marriages, the vast majority of violent marriages end in divorce, and employment rates are lower for women who experience abuse. We then construct a sequential model of employment, marriage and abuse. The results indicate abuse is the primary factor in the decision to divorce and witnessing violence as a child is a strong predictor of becoming an abusive spouse. Policy experiments suggest men are more responsive to policies designed to increase the costs of abuse than women are to policies reducing the cost of leaving violent marriages and policies designed to reduce the inter-generational effects of domestic violence may be promising strategies for preventing abuse.Domestic Violence, Abuse, Employment, Marriage, Divorce

Especiallly the Mulato Ones Like to Dance” Cuban Films and Discourses of Ethnic Difference

This paper examines the meaning of ethnicity in contemporary Cuba. By conceptualizing inequality as structured in both the public and private realms of society, I argue that the private realm should be given equal weight in social research on ethnic inequality. The paper differentiates between structural inequality in the public realm, which has been largely addressed by the previous literature on Cuban society, and the meaning of ethnic difference at the cultural level, which shapes the nature of social interactions in the private realm. Drawing on both the sociology of culture and cinema studies, I analyze Cuban films for representations and discourses of ethnic difference. As expressive cultural forms, films are not merely reflective of an “objective” meaning of ethnicity in society, but rather are part of a more complex process of interpretation, expression, and creation of meaning. Initial findings reveal the persistence of ethnic distinctions in the private realm of Cuban society, despite a strong political rhetoric and official state policy of ethnic equality. That ethnic distinctions can persist despite little evidence of structural inequality indicates a discontinuity between structural-level change and cultural change, and suggests the possibility of deepening ethnic inequality as Cuba transitions to a new economic/political arrangement

Effects of social disruption in elephants persist decades after culling.

BACKGROUND Multi-level fission-fusion societies, characteristic of a number of large brained mammal species including some primates, cetaceans and elephants, are among the most complex and cognitively demanding animal social systems. Many free-ranging populations of these highly social mammals already face severe human disturbance, which is set to accelerate with projected anthropogenic environmental change. Despite this, our understanding of how such disruption affects core aspects of social functioning is still very limited. RESULTS We now use novel playback experiments to assess decision-making abilities integral to operating successfully within complex societies, and provide the first systematic evidence that fundamental social skills may be significantly impaired by anthropogenic disruption. African elephants (Loxodonta africana) that had experienced separation from family members and translocation during culling operations decades previously performed poorly on systematic tests of their social knowledge, failing to distinguish between callers on the basis of social familiarity. Moreover, elephants from the disrupted population showed no evidence of discriminating between callers when age-related cues simulated individuals on an increasing scale of social dominance, in sharp contrast to the undisturbed population where this core social ability was well developed. CONCLUSIONS Key decision-making abilities that are fundamental to living in complex societies could be significantly altered in the long-term through exposure to severely disruptive events (e.g. culling and translocation). There is an assumption that wildlife responds to increasing pressure from human societies only in terms of demography, however our study demonstrates that the effects may be considerably more pervasive. These findings highlight the potential long-term negative consequences of acute social disruption in cognitively advanced species that live in close-knit kin-based societies, and alter our perspective on the health and functioning of populations that have been subjected to anthropogenic disturbance

Half-magnetization plateaux in Cr spinels

Magnetization plateaux, visible as anomalies in magnetic susceptibility at low temperatures, are one of the hallmarks of frustrated magnetism. An extremely robust half-magnetization plateau is observed in the spinel oxides CdCr2O4 and HgCr2O4, where it is accompanied by a substantial lattice distortion. We give an overview of the present state experiment for CdCr2O4 and HgCr2O4, and show how such a half-magnetization plateau arises quite naturally in a simple model of these systems, once coupling to the lattice is taken into account.Comment: 8 pages latex using IOP macros, from review talk given at RHMF 2006 (Sendai

Electronic properties of the pseudogap system (TaSe4)2I

The room temperature ``metallic'' properties of the quasi-one-dimensional charge density wave system (TaSe4)2I differ markedly from those expected of either a Fermi or a Luttinger Liquid. We discuss evidence for the simplest possible explanation of the observed behavior of (TaSe4)2I in its conducting phase - namely the existence of large quasi-static fluctuations of structural order, which however remain of finite extent above the charge density wave transition temperature. These fluctuations produce a pseudogap in the density of states. We compute the temperature dependence of the optical and DC conductivities of (TaSe4)2I in its conducting phase, the nature of its core hole spectra, and the NMR relaxation rate. Predictions for these quantities are made on the basis of a Lee, Rice and Anderson model. This model represents the simplest theory of a pseudogap, and gives satisfactory agreement with experiment in the cases where comparisons can be made. In contrast, the predictions of a strongly correlated (Luttinger Liquid) model appear to to contradict the data. The chief remaining discrepancy is that the gap appearing in transport quantities is less than that observed in photoemission. We discuss some possibilities for resolving this issue.Comment: 41 pages latex, 11 ps figures, uses IOP macro

Clinical Presentation and Treatment Outcomes of Children and Adolescents with Low Back Pain in Physical Therapy

Purpose: Low back pain (LBP) is a common condition in adolescents, and a specific pathoanatomical origin for the symptoms cannot always be determined. The purpose of this work was to examine the clinical presentation and outcomes of rehabilitation for adolescents with LBP. Methods: This study was completed in three phases. Phase 1 was a retrospective review of 25 patients under the age of 18 who were seen for treatment of LBP. Information regarding the patients' diagnoses, history, examination, and outcome were collected from chart review. Phase 2 was a review of 99 patients under the age of 18 with LBP. Numerical Pain Rating Scale (NPRS) and the Modified Oswestry Questionnaire (OSW) were recorded. Phase 3 consisted of a prospective study of treatment-based classification (TBC) of 34 adolescent patients seen in physical therapy for LBP. Treatment duration and content were at the clinician's discretion. Patients completed an OSW and NPRS before and after physical therapy. Patients were classified using a TBC algorithm, and effectiveness of classification on outcome was examined. Results: In study 1, initial pain scores were lower if a specific pathology was present (P=.001). Initial pain and OSW scores were poorly correlated (r= 0.16). 44% (n=11) of patients scored under the floor value of 12% on OSW. A second examination of the OSW in study 2 concluded that OSW was moderately correlated with NPRS (0.59). Chronbach's alpha was 0.86. All 10 items in OSW appeared to load onto two latent factors. In study 3, a classification decision was able to be made with a moderate degree of reliability (0.53 (0.28, 0.79) ≤ κ ≤ 0.89 (.74, 1.0)) in all of the 34 patients. Stabilization was the most commonly prescribed treatment by clinicians. Those who were matched to their TBC classification experienced fewer numbers of visits than those who were not. Conclusions: It appears the OSW is a valid and reliable tool for assessing clinical outcome of physical therapy intervention for adolescents with LBP. These results also suggest that a TBC approach to treatment of LBP in this population may be effective for improvements in clinical outcome

The Racial Politics of Elementary School Choice for Black Parents Living in Brooklyn, NY

Charter school proliferation has disproportionately affected Black urban neighborhoods and the debate about the relationship between racial educational equity and enhanced public school choice through charters has created dissension and discord in scholarship and across Black politics, educational organizing efforts, neighborhoods, and school communities. This study is an interpretive policy analysis of the effects of charter school policy on the elementary school choice preferences and experiences of twenty Black parents living in predominately low-income and racially segregated Black Brooklyn neighborhoods where charter schools are disproportionately concentrated. It was designed to identify disparities between the values and goals of school choice policy and the values, goals, and racialized experiences of Black parents engaging in school choice. Each stage of analysis compared and contrasted dominant narratives about choice and public schools with Black parents’ school choice narratives, which constitute an experience-based racial politics of school choice. The analysis identified common racialized challenges Black urban American parents confronted, regardless of class or ethnicity, and compared and contrasted their diverse responses to these challenges to conceptualize a Black standpoint from which to perceive the consequences, limitations, and promise of school choice policy. Parents who participated in this study internalized and subverted dominant narratives about public school crisis and choice. They discursively valued private schooling over public while also acknowledging a cultural hierarchy of public schools wherein public schools like charters and traditional public schools located in relatively wealthier and Whiter neighborhoods were ascribed with far more symbolic exchange value than their public neighborhood schools. They perceived choice as a means of escape from neighborhood disadvantage related to concentrated urban poverty and what they believed to be their low-income neighbors’ cultural poverty. This finding is counter to the logic undergirding the charter sector’s choice to disproportionately concentrate charters in Black neighborhoods. Parents also held a related generational belief and had internalized the dominant narrative of engaging in choice as good parenting, and perceived parents of children in private and public schools of choice as invested and involved and parents with children in their neighborhood public schools as ignorant, unmotivated, entitled, and/or uninvolved. Relatedly, they perceived choice as a means to join social networks of parents in culturally valued schools where parents have more capital, and further revealed assumptions of neighborhood cultural deficit and significant intra-racial, –neighborhood, and –school community social ruptures. Parents also internalized the dominant narrative of the purpose of schooling as preparation for college and careers in an increasingly competitive global society and perceived school choice as a means to dominant cultural capital acquisition. That said, they believed that different classes needed different educational training to meet this end and demanded a diversification of educational models in their neighborhoods. Regardless of class, parents expressed a strong preference for “diverse” schools as a means to meet the end of dominant cultural capital acquisition, a term that seemed to serve as proxy for Whiteness in most accounts. This finding challenges the concept of Black “self-segregation” through preference for and choice of ethnocentric school models. Finally, some parents’ preferences shifted with social changes or school’s admissions policy or location changes, revealing that parents’ preferences are as unfixed and mutable as the school choice marketplaces they engage in. Further, many parents experienced choice as an iterative and ongoing process. While charter policy enhanced parents’ opportunities to escape and choose public and private schools, they did not find this to be a liberating, empowering, or equitable experience. On the contrary, parents found elementary school mobility to be a confounding, depleting, and guilt- and anxiety-ridden experience. These parents’ school choice stories are an urgent reminder that any reforms to charter school policy must be complimented with reforms to all elements of the public school choice marketplace and that they and their children would not have incurred racialized costs of school choice had any of the twenty parents who participated in this study perceived and/or experienced their neighborhood public school to be a reasonable option