The Incidence of Geography on Canada's Services Trade

We estimate geographic barriers to export trade in nine service categories for Canada's provinces from 1997 to 2007 using the structural gravity model. Constructed Home, Domestic and Foreign Bias indexes (the last two new) capture the direct plus indirect effect of services trade costs on intra-provincial, inter-provincial and international trade relative to their frictionless benchmarks. Barriers to services international trade are huge relative to inter-provincial trade and large relative to goods international trade. A novel test confirms the fit of structural gravity with services trade data.

Non Magnetic Impurities in the Spin-Gap Phase of the Cuprate

It is now well established that Zn doping of high-$T_C$ cuprates reduces their $T_C$ and triggers the appearence of a spin glass phase. In this context, we have solved exactly the problem of N non magnetic impurities in the staggered flux phase of the Heisenberg model which we assume to be a good mean-field approximation for the spin-gap phase of the cuprates. In this model, the quasiparticule spectrum has four nodes on the Fermi surface, and linearization of the spectrum in the neighbourhood of these nodes leads to a system of 2D Dirac fermions. In the presence of a macroscopic number of (non magnetic) impurities, the problem has a characteristic logarithmic structure that renders ineffective the usual perturbative expansions. We have used this logarithmic structure to calculate an exact solution. For a concentration ni of impurities in the unitary scattering limit, the additional density of states is found to be proportional to $ni/(w \ln^2 (|w|/D))$ (where D is the infrared cut-off of the linearized spectrum) in analogy with the 1D case of doped spin-Peierls and two-leg ladders compounds. We argue that the system exhibits a quasi long-range order at T=0 with instantaneous spin-spin correlations decreasing as $ni/ \ln^4 (ni/R_{ij})$ for large distances $R_{ij}$ between impurity sites. We predict enhanced low energy fluctuations and compare these results to NMR and inelastic neutron scattering experiments in the high-$T_C$ cuprates.Comment: proceeding of SCES98 conference in Paris, July '9

The Braincase of Eocaecilia micropodia (Lissamphibia, Gymnophiona) and the Origin of Caecilians

The scant fossil record of caecilians has obscured the origin and evolution of this lissamphibian group. Eocaecilia micropodia from the Lower Jurassic of North America remains the only stem-group caecilian with an almost complete skull preserved. However, this taxon has been controversial, engendering re-evaluation of traits considered to be plesiomorphic for extant caecilians. Both the validity of the placement of E. micropodia as a stem caecilian and estimates of the plesiomorphic condition of extant caecilians have been questioned. In order to address these issues, the braincase of E. micropodia was examined via micro-computed tomography. The braincase is considered to be a more reliable phylogenetic indicator than peripheral regions of the skull. These data reveal significant new information, including the possession of an ossified nasal septum, ossified anterior wall of the sphenethmoid, long anterolateral processes on the sphenethmoid, and paired olfactory nerve foramina, which are known only to occur in extant caecilians; the latter are possibly related to the evolution of the tentacle, a caecilian autapomorphy. A phylogenetic analysis that included 64 non-amniote taxa and 308 characters represents the first extensive test of the phylogenetic affinities of E. micropodia. The results place E. micropodia securely on the stem of extant caecilians, representing a clade within Temnospondyli that is the sister taxon to batrachians plus Gerobatrachus. Ancestral character state reconstruction confirms the braincase of E. micropodia to be largely representative of the plesiomorphic condition of extant caecilians. Additionally, the results refine the context within which the evolution of the caecilian form can be evaluated. The robust construction and pattern of the dermal skull of E. micropodia is interpreted as symplesiomorphic with advanced dissorophoid temnospondyls, rather than being autapomorphic in its robust construction. Together these data increase confidence in incorporating E. micropodia into discussions of caecilian evolution.Organismic and Evolutionary Biolog

In Print

Faculty authors explore Spanish vanguard poetry, fatherhood, multi-modal learning, and more

The speaking vocabulary of 454 third grade children.

Thesis (Ed.M.)--Boston Universit

Orbiter Boundary Layer Transition Prediction Tool Enhancements

Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations

Genetic Characterization of H3N2 Influenza Viruses Isolated from Pigs in North America, 1977–1999: Evidence for Wholly Human and Reassortant Virus Genotypes

Since 1998, H3N2 viruses have caused epizootics of respiratory disease in pigs throughout the major swine production regions of the U.S. These outbreaks are remarkable because swine influenza in North America had previously been caused almost exclusively by H1N1 viruses. We sequenced the full-length protein coding regions of all eight RNA segments from four H3N2 viruses that we isolated from pigs in the Midwestern U.S. between March 1998 and March 1999, as well as from H3N2 viruses recovered from a piglet in Canada in January 1997 and from a pig in Colorado in 1977. Phylogenetic analyses demonstrated that the 1977 Colorado and 1997 Ontario isolates are wholly human influenza viruses. However, the viruses isolated since 1998 from pigs in the Midwestern U.S. are reassortant viruses containing hemagglutinin, neuraminidase and PB1 polymerase genes from human influenza viruses, matrix, non-structural and nucleoprotein genes from classical swine viruses, and PA and PB2 polymerase genes from avian viruses. The HA proteins of the Midwestern reassortant swine viruses can be differentiated from those of the 1995 lineage of human H3 viruses by 12 amino acid mutations in HA1. In contrast, the Sw:ONT:97 virus, which did not spread from pig-to-pig, lacks 11 of these changes

Methods for analyzing the concentration and speciation of major and trace elements in marine particles

Particles influence trace element and isotope (TEI) cycles through both their elemental composition and fate and their role on the partitioning of dissolved elements through scavenging and dissolution. Because of their complex compositions, a diverse suite of methods is required to analyze marine particles. Here we review some of the varied approaches used to study particle composition, speciation and fate. We focus on high throughput analytical methods that are useful for the international GEOTRACES program, and we also describe new spectroscopic techniques that are now being applied to study the spatial distribution and chemical speciation of TEIs in marine particles

The Perils of Recreational Marijuana Use: Relationships With Mental Health Among Emergency Department Patients

Abstract Introduction Marijuana is a commonly used drug in the United States. Many states have legalized the recreational use of marijuana. The effects of marijuana on mental health are unknown. Methods In this prospective survey study, eligible participants included ED patients age 18 and older, who had ever used recreational marijuana. A survey instrument was developed, piloted, and revised. Data collected included reasons for marijuana use, marijuana\u27s perceived effectiveness, and history of mental health conditions, including depression, anxiety, and suicidal thoughts. Results Among 303 participants (86% response rate), the median age of first marijuana use was 16 ([IQR 14, 19], range 6–65). The most commonly cited reasons for marijuana use included recreational use (70%; n = 211), to treat anxiety (30%; n = 89), to treat pain (25%; n = 74), and to treat depression (17%; n = 51). Mental health issues were common in the study population. A majority of patients reported anxiety in the last 30 days (59%; n = 176), and a significant minority of patients reported serious depression in the last 30 days (46%; n = 137). Some patients reported suicidal thoughts in the last 30 days (9%; n = 29). Participants who used marijuana more frequently reported more days of anxiety (median 15.5, compared to 1; P = 0.001). Among participants with mental health conditions, most began using marijuana before the onset of the mental health conditions (77%, n = 167). Earlier age of starting to use marijuana was correlated with higher number of years of anxiety or tension in lifetime (r = −0.11, P = 0.05, n = 301). Perceived effects of marijuana use on mental health were variable. Most participants stated that marijuana improved their mental health (62%; n = 163), and some reported that marijuana did not improve their mental health (37%; n = 98). Conclusions Many ED patients have used marijuana, either currently or in the past. Mental health conditions are also common, including anxiety, depression, and suicidal thoughts. Most participants reported marijuana use starting at an age under 18. Marijuana use preceded the onset of mental health conditions in the majority of participants

Effect of Company-Driven Disability Diversity initiatives: A multi-case study across industries

OBJECTIVE: In this article, we share insights emerging from case studies conducted across seven companies.We illustrate the motives, processes, and outcomes of these initiatives. METHODS: This study is built on the previously published case studies conducted across seven companies. We applied elements of consensual qualitative research (CQR) for the data collection and analyses before performing an in-depth qualitative content analysis using the data coded for each company, looking for commonalities and differences. RESULTS: Although practices differed, all companies experienced noted benefits. Committed leadership and complementary company values facilitated successful outcomes for initiatives. The strength or salience of disability-inclusive actions and practices appeared to moderate outcomes related to company performance, employee perceptions of the company, and cohesiveness. CONCLUSION: Company disability initiatives can yield positive impacts on company performance and culture. The practices we identified and their positive outcomes serve as beacons to other organizations that recognize disability as a valued part of company diversity