Alterations in immunoglobulin levels in uninfected children born to HIV infected women

Background Immunoglobulin levels are known to be elevated in HIV infected children. However, little is known about the effect of maternal HIV infection and the maternal altered immune system on immunoglobulin levels in uninfected children. As few data are available on immunoglobulins from young healthy children, we used data from uninfected children born to hepatitis C virus (HCV) infected women as a comparison. Methods Prospective data on immunoglobulin levels were available from birth to 5 years for children enrolled in the European Collaborative Study (ECS) of children born to HIV-1 infected women and from birth to 24 months for children enrolled in the European Paediatric HCV Network (EPHN). Children born to HIV/HCV co-infected women were excluded. Smoothers (running means) illustrated patterns of immunoglobulins over age by infection status. Associations between infant and maternal factors and child log10 total IgG, IgM and IgA levels were quantified in linear regression analyses allowing for repeated measures within child. Further analyses were performed using only data of HIV exposed uninfected children to investigate associations between child immunoglobulins and maternal immunological and virological factors and anti-retroviral therapy exposure. Results 1751 HIV uninfected, 190 HIV infected children (ECS), 173 HCV uninfected and 30 HCV infected children (EPHN) were included. HIV infected children had higher levels of all immunoglobulins compared to uninfected children over all ages. HIV uninfected children had significantly higher IgG, IgM and IgA levels than HCV uninfected children upto at least 24 months, adjusting for gender, prematurity and race. Prematurity was associated with significantly lower levels of immunoglobulins upto 24 months. Children born to African women had higher IgG and IgA levels upto 24 months than those born to white women but lower IgM in the first 6 months. Among HIV uninfected children higher IgG levels were associated with elevated maternal IgG levels, as well for measurements from 18 months to 5 years of age. No significant effect of maternal CD4 count was observed. ART exposure was associated with significantly lower IgG levels at 6-24 months. Race was not associated with immunoglobulin levels in multivariable analyses in this sub-group. Conclusions These findings indicate significant alterations in immunoglobulin levels in uninfected children born to HIV infected women. This suggests that exposure to an activated maternal immune system is associated with an altered humoral response in children without antigen stimulation, and warrants further research

SPH Simulations of Direct Impact Accretion in the Ultracompact AM CVn Binaries

The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527) - a two-member subclass of the AM CVn stars - continue to pique interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three is significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs (2002), in which the accretion stream impacts the surface of a rapidly-rotating primary white dwarf directly but at a near-glancing angle. One requirement of this model is that the accretion stream have a high enough density to advect its specific kinetic energy below the photosphere for progressively more-thermalized emission downstream, a constraint that requires an accretion spot size of roughly 1.2x10^5 km^2 or smaller. Having at hand a smoothed particle hydrodynamics code optimized for cataclysmic variable accretion disk simulations, it was relatively straightforward for us to adapt it to calculate the footprint of the accretion stream at the nominal radius of the primary white dwarf, and thus to test this constraint of the direct impact model. We find that the mass flux at the impact spot can be approximated by a bivariate Gaussian with standard deviation \sigma_{\phi} = 164 km in the orbital plane and \sigma_{\theta} = 23 km in the perpendicular direction. The area of the the 2\sigma ellipse into which 86% of the mass flux occurs is roughly 47,400 km^2, or roughly half the size estimated by Marsh & Steeghs (2002). We discuss the necessary parameters of a simple model of the luminosity distribution in the post-impact emission region.Comment: 24 pages, 5 figures, Accepted for publication in Ap

VLBI observations of jupiter with the initial test station of LOFAR and the nancay decametric array

AIMS: To demonstrate and test the capability of the next generation of low-frequency radio telescopes to perform high resolution observations across intra-continental baselines. Jupiter's strong burst emission is used to perform broadband full signal cross-correlations on time intervals of up to hundreds of milliseconds. METHODS: Broadband VLBI observations at about 20 MHz on a baseline of ~50000 wavelengths were performed to achieve arcsecond angular resolution. LOFAR's Initial Test Station (LOFAR/ITS, The Netherlands) and the Nancay Decametric Array (NDA, France) digitize the measured electric field with 12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter's signal was used for data synchronization prior to correlation on the time-series data. RESULTS: Strong emission from Jupiter was detected during snapshots of a few seconds and detailed features down to microsecond time-scales were identified in dynamic spectra. Correlations of Jupiter's burst emission returned strong fringes on 1 ms time-scales over channels as narrow as a hundred kilohertz bandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at low frequencies, in spite of phase shifts introduced by variations in ionospheric propagation characteristics. Phase coherence was preserved over tens to hundreds of milliseconds with a baseline of ~700 km. No significant variation with time was found in the correlations and an estimate for the fringe visibility of 1, suggested that the source was not resolved. The upper limit on the source region size of Jupiter Io-B S-bursts corresponds to an angular resolution of ~3 arcsec. Adding remote stations to the LOFAR network at baselines up to thousand kilometers will provide 10 times higher resolution down to an arcsecond.Comment: 6 pages, 4 figures. Nigl, A., Zarka, P., Kuijpers, J., Falcke, H., Baehren, L., VLBI observations of Jupiter with the Initial Test Station of LOFAR and the Nancay Decametric Array, A&A, 471, 1099-1104, accepted on 31/05/200

Fast Magnetosonic Waves Driven by Gravitational Waves

The propagation of a gravitational wave (GW) through a magnetized plasma is considered. In particular, we study the excitation of fast magnetosonic waves (MSW) by a gravitational wave, using the linearized general-relativistic hydromagnetic equations. We derive the dispersion relation for the plasma, treating the gravitational wave as a perturbation in a Minkowski background space-time. We show that the presence of gravitational waves will drive magnetosonic waves in the plasma and discuss the potential astrophysical implications.Comment: 12 pages, 2 figures, Astronomy and Astrophysics in pres

EUVE J0425.6-5714: A Newly Discovered AM Herculis Star

We detected a new AM Her star serendipitously in a 25 day observation with the EUVE satellite. A coherent period of 85.82 min is present in the EUVE Deep Survey imager light curve of this source. A spectroscopic identification is made with a 19th magnitude blue star that has H and He emission lines, and broad cyclotron humps typical of a magnetic cataclysmic variable. A lower limit to the polar magnetic field of 46 MG is estimated from the spacing of the cyclotron harmonics. EUVE J0425.6-5714 is also detected in archival ROSAT HRI observations spanning two months, and its stable and highly structured light curve permits us to fit a coherent ephemeris linking the ROSAT and EUVE data over a 1.3 yr gap. The derived period is 85.82107 +/- 0.00020 min, and the ephemeris should be accurate to 0.1 cycles until the year 2005. A narrow but partial X-ray eclipse suggests that this object belongs to the group of Am Her stars whose viewing geometry is such that the accretion stream periodically occults the soft X-ray emitting accretion spot on the surface of the white dwarf. A non-detection of hard X-rays from ASCA observations that are contemporaneous with the ROSAT HRI shows that the soft X-rays must dominate by at least an order of magnitude, which is consistent with a known trend among AM Her stars with large magnetic field. This object should not be confused with the Seyfert galaxy 1H 0419-577 (= LB 1727), another X-ray/EUV source which lies only 4' away, and was the principal target of these monitoring observations.Comment: 13 pages, 5 figures, to appear in PASP, Dec. 1998 issu

Potential Impacts of the Montreal Protocol Kigali Amendment to the Choice of Refrigerant Alternatives

The paper first gives a description of the “ Kigali Amendment” established HFC phase-down as decided by the Montreal Protocol parties in Kigali, Rwanda, October 2016. Baselines, freeze dates, schedules for the reductions of HFC consumption for both developing and developed country groups, as well as the 17 HFCs that are now included in the Montreal Protocol are summarized. The list of alternatives for HCFC- 22 including high-GWP HFC replacements is given, and considerations regarding the choice of refrigerant, both low-GWP synthetic and “natural” refrigerant alternatives are presented. The low-GWP refrigerant flammability issue and the performance of equipment at high ambient regions are described. It is discussed whether the potential impacts of the Kigali Amendment will be reinforcing the momentum of applications using low-GWP refrigerants and the innovation for sustainable RACHP technologie

Simulation of Fractionated Electrograms at Low Spatial Resolution in Large-Scale Heart Models

Abstract To compute extracellular potentials from transmembrane potentials an elliptic boundary-value problem must be solved. This must be done at a spatial resolution of 0.2 mm or better to avoid artefacts in the form of large spikes before and after major deflections. For macroscopic heart models, this leads to very large linear systems. Artefacts in low-resolution solutions are related to the restriction operator that is used to translate the sources from high to low resolution. Typically, this restriction is done by injecting transmembrane potentials. We propose to use transmembrane current as a source, with weighted summation rather than simple injection. We tested this method in a model of the human ventricles. We found that using the proposed scheme, a good visual match could be obtained between electrograms computed at 1-mm and 0.2-mm resolution, even in regions where strong sub-millimeter heterogeneity in tissue conductivity was present. Introduction Computation of extracellular potentials from transmembrane potentials is a common problem in cardiac electrophysiology Artefacts in low-resolution solutions are related to the restriction operator that is used to translate the source data from the high-resolution to the low-resolution mesh. Typically, this restriction is done by injecting transmembrane potentials. We propose to use transmembrane current as a source, with regional summation rather than simple injection. The summation algorithm must fulfill the following criteria: • No contribution may be lost, otherwise a solution for the linear problem would not exist. • Contributions should remain as local as possible. • The summation should not introduce artefacts. We tested the performance of a summation method with trilinear weighting to fulfill these criteria. Methods An anatomic model of a human heart and torso was created from MRI data as described earlier The resulting model represented the subject's heart with 50 million cubic elements having sides of 0.2 mm. To each element, a local fiber orientation and cell type (subendocardial, subepicardial, or M cell) were assigned. Propagating action potentials (AP) were simulated with a monodomain reaction-diffusion equation, using software that has been described previously Computation of extracellular potentials (electrograms) from the simulated membrane potentials was based on the bidomain model for cardiac tissue where We evaluated I(x, t) at the full 0.2 mm resolution of the reaction-diffusion model. Uniform finite-difference meshes were used for both the simulation of propagation and for the computation of φ e (x, t). To solve equation where N is the ratio of fine to coarse grid resolution (N = 5 in this paper) and ∆x, ∆y, ∆z is the number of finemesh edges between the C node and the F node along the x, y, and z axis, respectively. Thus, both the sum of all weights for a single C node and the sum of the weights for a single F node were unity. To obtain a unique solution to equation Electrograms were computed at 1-mm resolution both for the isolated heart and for the in-situ heart. These simulations were performed with 1 million and with 42 million nodes, respectively. To test the validity of the lowresolution results, electrograms were also computed at the full 0.2-mm resolution in the isolated heart; this took 113 million nodes. Simulations were performed on 32-128 processors of an SGI Altix 4700 supercomputer. To create a situation where inhomogeneous tissue caused fractionated electrograms, fibrofatty replacement and Na-channel block were simulated as in previous work 3. Results Discussion and conclusions We have shown that using regionally summated transmembrane current as a source, electrograms may be computed at a resolution as low as 1 mm in a model of the human ventricles without introducing visible artefacts. Assuming that the transmembrane current itself is computed with a reaction-diffusion model at 0.2-mm to 0.1-mm resolution, this reduces the computational load associated with electrogram simulation by at least a factor 125 to 1000. The proposed method is easy to implement in an existing bidomain solver. It worked well even in the presence of sub-millimeter heterogeneity in tissue conductivity. The method is probably less accurate in small-scale simulations, where most of the electrogram shape originates from nearby tissue. We consider it useful for whole-heart and whole-body models of large mammals, especially man. It may also be valuable as a restriction operator in (geometric) multigrid methods