A Search for Companions to Brown Dwarfs in the Taurus and Chamaeleon Star Forming Regions

We present the results of a search for companions to young brown dwarfs in the Taurus and Chamaeleon I star forming regions (1/2-3 Myr). We have used WFPC2 on board HST to obtain F791W and F850LP images of 47 members of these regions that have spectral types of M6-L0 (0.01-0.1 Msun). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. We have applied PSF subtraction to the primaries and have searched the resulting images for objects that have colors and magnitudes that are indicative of young low-mass objects. Through this process, we have identified promising candidate companions to 2MASS J04414489+2301513 (rho=0.105"/15 AU), 2MASS J04221332+1934392 (rho=0.05"/7 AU), and ISO 217 (rho=0.03"/5 AU). We reported the discovery of the first candidate in a previous study, showing that it has a similar proper motion as the primary through a comparison of astrometry measured with WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon, and Upper Sco (10 Myr), we measure binary fractions of 14/93 = 0.15+0.05/-0.03 for M4-M6 (0.1-0.3 Msun) and 4/108 = 0.04+0.03/-0.01 for >M6 (10 AU. Given the youth and low density of these three regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.Comment: Astrophysical Journal, in pres

Expression of DC-SIGN and DC-SIGNRs in placentas of HIV-positive patients

Background. Human dendritic cell-specific intracellular adhesion molecule-3 (ICAM3)-grabbing non-integrin (DC-SIGN) is a mannose-binding lectin that initiates interaction between dendritic cells and resting T-lymphocytes. DC-SIGN is highly expressed in placental tissue on dendritic cells and Hofbauer cells, and it is suggested that HIV may become adsorbed to DC-SIGN on Hofbauer cells as part of the mechanism of mother-to-child HIV transmission. A possible mechanism of transfer of the virus from the Hofbauer cells to the fetus is the subsequent adsorption to DC-SIGN-related molecules (DC-SIGNRs), present on immediately adjacent capillary vascular endothelium. However, data on DC-SIGN and DC-SIGNR expression in the placenta are few. Methods. Forty term placentas from HIV-positive mothers and 21 term placentas from HIV-negative mothers underwent immunohistochemistry staining for DC-SIGN and DC-SIGNR expression. Five random sets of 10 villi were assessed, and the average number of positive cells were counted in each case. In addition, where possible, maternal and cord blood viral loads and maternal CD4+ counts were performed in the HIV-positive group only. Results. The median maternal CD4+ count was 377 cells/μl and 27% of participants had undetectable viral loads; the median detectable viral load was 3.72 log. Most (97%) of the cord bloods tested in infants from HIV-positive mothers had lower than detectable viral loads. HIV-positive cases had significantly greater expression of both DC-SIGNRs (median values in HIV-positive cases, 14.5 positive cells/10 villi (pc/10villi), compared with 11 pc/10villi in HIV-negative cases, p=0.020) and DC-SIGN (median value in HIV-positive cases, 26.5 pc/10villi, compared with 23 pc/10villi in HIV-negative cases, p=0.037). DC-SIGNR expression was also noted in Hofbauer cells and decidual macrophages in addition to endothelium (reported currently). There was no difference in expression of DC-SIGN and DC-SIGNRs in patients with or without chorioamnionitis, but there was an inverse relationship between DC-SIGN and DC-SIGNR expression and maternal CD4+ counts in HIV-positive cases. Conclusion. Both DC-SIGN and DC-SIGNR expression were higher in placentas from HIV-positive mothers compared with HIV-negative cases. These lectins may be potential new therapeutic targets for preventing vertical transmission of HIV

Transcutaneous measurement of volume blood flow

Blood flow velocity measurements, using Doppler velocimeter, are described. The ability to measure blood velocity using ultrasound is derived from the Doppler effect; the change in frequency which occurs when sound is reflected or transmitted from a moving target. When ultrasound of the appropriate frequency is transmitted through a moving blood stream, the blood cells act as point scatterers of ultrasonic energy. If this scattered ultrasonic energy is detected, it is found to be shifted in frequency according to the velocity of the blood cells, nu, the frequency of the incident sound, f sub o, the speed of sound in the medium, c, and the angle between the sound beam and the velocity vector, o. The relation describing this effect is known as the Doppler equation. Delta f = 2 f sub o x nu x cos alpha/c. The theoretical and experimental methods are evaluated

Development of ultrasonic methods for hemodynamic measurements

A transcutanous method to measure instantaneous mean blood flow in peripheral arteries of the human body was defined. Transcutanous and implanted cuff ultrasound velocity measurements were evaluated, and the accuracies of velocity, flow, and diameter measurements were assessed for steady flow. Performance criteria were established for the pulsed Doppler velocity meter (PUDVM), and performance tests were conducted. Several improvements are suggested

Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials light propagation is unusual, leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride (hBN), a natural mid-infrared hyperbolic material, can act as a "hyper-focusing lens" and as a multi-mode waveguide. The lensing is manifested by subdiffractional focusing of phonon-polaritons launched by metallic disks underneath the hBN crystal. The waveguiding is revealed through the modal analysis of the periodic patterns observed around such launchers and near the sample edges. Our work opens new opportunities for anisotropic layered insulators in infrared nanophotonics complementing and potentially surpassing concurrent artificial hyperbolic materials with lower losses and higher optical localization.Comment: 25 pages, 5 figure

Quasars and Ultraluminous Infrared Galaxies: At the Limit?

We have detected the host galaxies of 16 nearby, radio-quiet quasars using images obtained with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). We confirm that these luminous quasars tend to live in luminous, early-type host galaxies, and we use the host-galaxy magnitudes to refine the luminosity/host-mass limit inferred from ground-based studies. If quasars obey the relation $M_{black hole}/M_{spheroid}\sim0.006$ found for massive dark objects in nonactive galaxies, then our analysis implies that they radiate at up to $\sim20$ of the Eddington rate. An analogous analysis for ultraluminous infrared galaxies shows them to accrete at up to similar Eddington fractions, consistent with the hypothesis that some of them are powered by embedded quasars.Comment: 9 pages, includes 2 eps figs, accepted to ApJLet

Feedback from massive stars at low metallicities : MUSE observations of N44 and N180 in the Large Magellanic Cloud

Accepted for publication in MNRAS, 27 pages, 21 figuresWe present MUSE integral field data of two HII region complexes in the Large Magellanic Cloud (LMC), N44 and N180. Both regions consist of a main superbubble and a number of smaller, more compact HII regions that formed on the edge of the superbubble. For a total of 11 HII regions, we systematically analyse the radiative and mechanical feedback from the massive O-type stars on the surrounding gas. We exploit the integral field property of the data and the coverage of the HeII$\lambda$5412 line to identify and classify the feedback-driving massive stars, and from the estimated spectral types and luminosity classes we determine the stellar radiative output in terms of the ionising photon flux $Q_{0}$. We characterise the HII regions in terms of their sizes, morphologies, ionisation structure, luminosity and kinematics, and derive oxygen abundances via emission line ratios. We analyse the role of different stellar feedback mechanisms for each region by measuring the direct radiation pressure, the pressure of the ionised gas, and the pressure of the shock-heated winds. We find that stellar winds and ionised gas are the main drivers of HII region expansion in our sample, while the direct radiation pressure is up to three orders of magnitude lower than the other terms. We relate the total pressure to the star formation rate per unit area, $\Sigma_{SFR}$, for each region and find that stellar feedback has a negative effect on star formation, and sets an upper limit to $\Sigma_{SFR}$ as a function of increasing pressure.Peer reviewe