Astrometric Limits on the Stochastic Gravitational Wave Background

The canonical methods for gravitational wave detection are ground- and space-based laser interferometry, pulsar timing, and polarization of the cosmic microwave background. But as has been suggested by numerous investigators, astrometry offers an additional path to gravitational wave detection. Gravitational waves deflect light rays of extragalactic objects, creating apparent proper motions in a quadrupolar (and higher-order modes) pattern. Astrometry of extragalactic radio sources is sensitive to gravitational waves with frequencies between roughly $10^{-18}$ and $10^{-8}$ Hz ($H_0$ and 1/3 yr$^{-1}$), overlapping and bridging the pulsar timing and CMB polarization regimes. We present a methodology for astrometric gravitational wave detection in the presence of large intrinsic uncorrelated proper motions (i.e., radio jets). We obtain 95% confidence limits on the stochastic gravitational wave background using 711 radio sources, $\Omega_{GW} < 0.0064$, and using 508 radio sources combined with the first Gaia data release: $\Omega_{GW} < 0.011$. These limits probe gravitational wave frequencies $6\times10^{-18}$ Hz $\lesssim f \lesssim 1\times10^{-9}$ Hz. Using a WISE-Gaia catalog of 567,721 AGN, we predict a limit expected from Gaia alone of $\Omega_{GW} < 0.0006$, which is significantly higher than was originally forecast. Incidentally, we detect and report on 22 new examples of optical superluminal motion with redshifts 0.13-3.89.Comment: 29 pages, 5 figures, ApJ in press. Updated to correspond to published versio

Not all farms are created equal: Shady African cocoa farms promote a richer bat fauna

Bats provide important pest suppression services with economic value to cocoa farmers, yet the impact of cocoa farm management on bat diversity metrics is still poorly understood. This is especially important if we consider that Afrotropical cocoa farms supply 68 % of the world's chocolate market, with expected increases in production in the forthcoming decades. In this study, we investigated for the first time how bat abundance, richness and diversity varied between African cocoa farms with different levels of shade tree cover, shade tree communities and cocoa characteristics. We found that shade tree cover and shade tree height were the main drivers associated with an increase of Shannon diversity, and abundance and richness of insectivores. Frugivorous and nectarivorous bats were positively associated with the presence of planted shade trees, but richness varied with the size of shade trees. The insectivorous Hipposideros fuliginosus was only present in high shade farms, being captured 51 times only in this shade system, while the frugivorous Myonycteris angolensis was associated with low shade farms. Our findings show that indeed not all farms are created equal, with high shade farms with large, tall forest shade trees (i.e., containing key plant resources) having richer bat communities. Therefore, policymakers seeking to conserve wildlife within cocoa farming systems should adopt cocoa management systems like those mentioned above and promote a combination of forest and planted shade trees to be able support a rich community of insectivorous, frugivorous and nectarivorous bats and maintain their associated ecosystems services

Factors associated with syphilis incidence in the HIV-infected in the era of highly active antiretrovirals.

After several years of steady decline, syphilis is reemerging globally as a public health hazard, especially among people living with human immunodeficiency virus (HIV). Syphilis resurgence is observed mainly in men who have sex with men (MSM), yet other transmission groups are affected too. In this manuscript, we study the factors associated with syphilis incidence in the Swiss HIV cohort study in the era of highly effective antiretrovirals. Using parametric interval censored models with fixed and time-varying covariates, we studied the immunological, behavioral, and treatment-related elements associated with syphilis incidence in 3 transmission groups: MSM, heterosexuals, and intravenous drug users. Syphilis incidence has been increasing annually since 2005, with up to 74 incident cases per 1000 person-years in 2013, with MSM being the population with the highest burden (92% of cases). While antiretroviral treatment (ART) in general did not affect syphilis incidence, nevirapine (NVP) was associated with a lower hazard of syphilis incidence (multivariable hazard ratio 0.5, 95% confidence interval 0.2-1.0). We observed that condomless sex and younger age were associated with higher syphilis incidence. Moreover, time-updated CD4, nadir CD4, and CD8 cell counts were not associated with syphilis incidence. Finally, testing frequency higher than the recommended once a year routine testing was associated with a 2-fold higher risk of acquiring syphilis. Condomless sex is the main driver of syphilis resurgence in the Swiss HIV Cohort study; ART and immune reconstitution provide no protection against syphilis. This entails targeted interventions and frequent screening of high-risk populations. There is no known effect of NVP on syphilis; therefore, further clinical, epidemiological, and microbiological investigation is necessary to validate our observation