Variability and origin of seismic anisotropy across eastern Canada: evidence from shear-wave splitting measurements

Measurements of seismic anisotropy in continental regions are frequently interpreted with respect to past tectonic processes, preserved in the lithosphere as “fossil” fabrics. Models of the present-day sublithospheric flow (often using absolute plate motion as a proxy) are also used to explain the observations. Discriminating between these different sources of seismic anisotropy is particularly challenging beneath shields, whose thick (≥200 km) lithospheric roots may record a protracted history of deformation and strongly influence underlying mantle flow. Eastern Canada, where the geological record spans ∼3 Ga of Earth history, is an ideal region to address this issue. We use shear wave splitting measurements of core phases such as SKS to define upper mantle anisotropy using the orientation of the fast-polarization direction ϕ and delay time δt between fast and slow shear wave arrivals. Comparison with structural trends in surface geology and aeromagnetic data helps to determine the contribution of fossil lithospheric fabrics to the anisotropy. We also assess the influence of sublithospheric mantle flow via flow directions derived from global geodynamic models. Fast-polarization orientations are generally ENE-WSW to ESE-WNW across the region, but significant lateral variability in splitting parameters on a ≤100 km scale implies a lithospheric contribution to the results. Correlations with structural geologic and magnetic trends are not ubiquitous, however, nor are correlations with geodynamically predicted mantle flow directions. We therefore consider that the splitting parameters likely record a combination of the present-day mantle flow and older lithospheric fabrics. Consideration of both sources of anisotropy is critical in shield regions when interpreting splitting observations

Impact of housing on the survival of persons with AIDS

<p>Abstract</p> <p>Background</p> <p>Homeless persons with HIV/AIDS have greater morbidity and mortality, more hospitalizations, less use of antiretroviral therapy, and worse medication adherence than HIV-infected persons who are stably housed. We examined the effect of homelessness on the mortality of persons with AIDS and measured the effect of supportive housing on AIDS survival.</p> <p>Methods</p> <p>The San Francisco AIDS registry was used to identify homeless and housed persons who were diagnosed with AIDS between 1996 and 2006. The registry was computer-matched with a housing database of homeless persons who received housing after their AIDS diagnosis. The Kaplan-Meier product limit method was used to compare survival between persons who were homeless at AIDS diagnosis and those who were housed. Proportional hazards models were used to estimate the independent effects of homelessness and supportive housing on survival after AIDS diagnosis.</p> <p>Results</p> <p>Of the 6,558 AIDS cases, 9.8% were homeless at diagnosis. Sixty-seven percent of the persons who were homeless survived five years compared with 81% of those who were housed (p < 0.0001). Homelessness increased the risk of death (adjusted relative hazard [RH] 1.20; 95% confidence limits [CL] 1.03, 1.41). Homeless persons with AIDS who obtained supportive housing had a lower risk of death than those who did not (adjusted RH 0.20; 95% CL 0.05, 0.81).</p> <p>Conclusion</p> <p>Supportive housing ameliorates the negative effect of homelessness on survival with AIDS.</p

Inhibition of immunoglobulin E synthesis through FcγRII (CD32) by a mechanism independent of B-cell receptor co-cross-linking

The inhibitory effect on antibody production by immune complexes has been shown to depend on co-ligation of the B-cell antigen receptor (BCR) with the low-affinity receptor for immunoglobulin G (IgG) (FcγRIIb, CD32). Here we report that immunoglobulin E (IgE) synthesis, induced in a BCR-independent manner by interleukin-4 (IL-4) and anti-CD40 antibody, was inhibited by CD32 ligation. The observed effect was specific for CD32 as, first, antibodies directed against other B-cell surface structures had no inhibitory effect, and, second, treatment with anti-CD32 of cells that had been in culture for 2 days was ineffective owing to the down-regulation of CD32 expression. IgE inhibition was also observed in cells stimulated by IL-4/CD40 F(ab′)(2) or IL-4 plus soluble CD40 ligand, demonstrating that co-cross-linking of CD32 and CD40 was not necessary to induce inhibition. Mechanistic studies into the IgE class switch process demonstrated that IL-4/anti-CD40-induced IgE germline gene transcription and B-cell proliferation were not affected by CD32 ligation. The data demonstrate that the negative regulatory role of the CD32 molecule is not restricted to BCR-induced B-cell activation, but is also functional on other B-cell activation pathways mediated by CD40 and IL-4

Ligand Strain and the Nature of Spin Crossover in Binuclear Complexes: Two-Step Spin Crossover in a 4,4′-Bipyridine-Bridged Iron(II) Complex [{Fe(dpia)(NCS) 2 } 2 (4,4′-bpy)] (dpia=di(2-picolyl)amine; 4,4′-bpy=4,4′-bipyridine)

International audienceThe synthesis and detailed characterization of the new spin crossover (SCO) binuclear complex [{Fe(dpia)(NCS)2}2(4,4′‐bpy)] (1; dpia=di(2‐picolyl)amine, 4,4′‐bpy=4,4′‐bipyridine) are reported. Variable‐temperature magnetic susceptibility measurements show a relatively cooperative two‐step spin transition suggesting the occurrence of three spin‐state isomers: [HS–HS], [HS–LS], and [LS–LS] (HS: high spin, LS: low spin). A short plateau at 204 K separates the two steps and conforms with about 50 % of the complexes having undergone a thermal spin conversion. Routine Mössbauer spectroscopy without applying a magnetic field clearly separates four iron(II) one‐center spin states in three [HS–HS], [HS–LS], and [LS–LS] pairs and unambiguously confirms that the spin transition at the plateau temperature goes through the intermediate [HS–LS] state. The single‐crystal X‐ray structure was solved for three spin isomers at 293, 208, and 120 K. The structural study at the plateau temperature was unable to resolve the HS and LS sites in the [HS–LS] pair and only an average Fe–N bond length was obtained, which suggests that there is an intermediate [HS–LS] phase. The structural analysis at three temperatures revealed a dense three‐dimensional network of both intra‐ and intermolecular interactions. The relative energies of the three spin‐state isomers were evaluated by quantum‐chemical DFT calculations. Comparison of compound 1 with previously known analogues, as well as the overall analysis of structural data for numerous binuclear complexes, allowed a conclusion to be reached on the crucial role of ligand strain effects in the SCO behavior of binuclear complexes. The suggested intramolecular mechanism explains the different types of SCO observed in binuclear complexes: one‐step, two‐step, and partial (50 %) transitions