Boundary Conditions of the Heliosphere

Radiative transfer equilibrium models of nearby interstellar matter (ISM) yield the boundary conditions of the heliosphere when constrained with observations of ISM inside and outside of the heliosphere. Filtration factors for interstellar neutrals crossing the heliosheath region, from charge exchange with interstellar plasma, are given for H, He, N, O, Ar, and Ne. The best models predict n(HI)~0.2 /cc, n(e)~0.1 /cc, however if the isotropic 2 kHz emission observed by Voyager (Kurth & Gurnett 2003) is formed in the surrounding ISM, an alternate model with lower electron densities is indicated. Observations of nearby ISM, the radiative transfer models, and historical 10Be records provide information on past variations in the galactic environment of the Sun

The Ionization of the Local Interstellar Medium, as Revealed by FUSE Observations of N, O and Ar toward White Dwarf Stars

FUSE spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495 and WD 2331-475 cover the absorption features out of the ground electronic states of N I, N II, N III, O I and Ar I in the far ultraviolet, providing new insights on the origin of the partial ionization of the Local Interstellar Medium (LISM), and for the case of G191-B2B, the interstellar cloud that immediately surrounds the solar system. Toward these targets the interstellar abundances of Ar I, and sometimes N I, are significantly below their cosmic abundances relative to H I. In the diffuse interstellar medium, these elements are not likely to be depleted onto dust grains. Generally, we expect that Ar should be more strongly ionized than H (and also O and N whose ionizations are coupled to that of H via charge exchange reactions) because the cross section for the photoionization of Ar I is very high. Our finding that Ar I/H I is low may help to explain the surprisingly high ionization of He in the LISM found by other investigators. Our result favors the interpretation that the ionization of the local medium is maintained by a strong EUV flux from nearby stars and hot gases, rather than an incomplete recovery from a past, more highly ionized condition.Comment: 13 pages, 2 figures. To appear in a special issue of the Astrophysical Journal Letters devoted to the first scientific results from the FUSE missio

The Boundary Conditions of the Heliosphere: Photoionization Models Constrained by Interstellar and In Situ Data

The boundary conditions of the heliosphere are set by the ionization, density and composition of inflowing interstellar matter. Constraining the properties of the Local Interstellar Cloud (LIC) at the heliosphere requires radiative transfer ionization models. We model the background interstellar radiation field using observed stellar FUV and EUV emission and the diffuse soft X-ray background. We also model the emission from the boundary between the LIC and the hot Local Bubble (LB) plasma, assuming that the cloud is evaporating because of thermal conduction. We create a grid of models covering a plausible range of LIC and LB properties, and use the modeled radiation field as input to radiative transfer/thermal equilibrium calculations using the Cloudy code. Data from in situ observations of He^O, pickup ions and anomalous cosmic rays in the heliosphere, and absorption line measurements towards epsilon CMa were used to constrain the input parameters. A restricted range of assumed LIC HI column densities and LB plasma temperatures produce models that match all the observational constraints. The relative weakness of the constraints on N(HI) and T_h contrast with the narrow limits predicted for the H^O and electron density in the LIC at the Sun, n(H^0) = 0.19 - 0.20 cm^-3, and n(e) = 0.07 +/- 0.01 cm^-3. Derived abundances are mostly typical for low density gas, with sub-solar Mg, Si and Fe, possibly subsolar O and N, and S about solar; however C is supersolar. The interstellar gas at the Sun is warm, low density, and partially ionized, with n(H) = 0.23 - 0.27 cm^-3, T = 6300 K, X(H^+) ~ 0.2, and X(He^+) ~ 0.4. These results appear to be robust since acceptable models are found for substantially different input radiation fields. Our results favor low values for the reference solar abundances for the LIC composition.Comment: 14 pages, 4 figures, submitted to Astronomy & Astrophysics together with papers from the International Space Sciences Institute workshop on Interstellar Hydrogen in the Heliospher

A noiseless kilohertz frame rate imaging detector based on microchannel plates read out with the Medipix2 CMOS pixel chip

A new hybrid optical imaging detector is described that is being developed for the next generation adaptive optics (AO) wavefront sensors (WFS) for ground-based telescopes. The detector consists of a photocathode and proximity focused microchannel plates (MCPs) read out by the Medipix2 CMOS pixel ASIC. Each pixel of the Medipix2 device measures 55x55 um2 and comprises pre-amplifier, a window discriminator and a 14-bit counter. The 256x256 Medipix2 array can be read out noiselessly in 287 us. The readout can be electronically shuttered down to a temporal window of a few us. The Medipix2 is buttable on 3 sides to produce 512x(n*256) pixel devices. Measurements with ultraviolet light yield a spatial resolution of the detector at the Nyquist limit. Sub-pixel resolution can be achieved using centroiding algorithms. For the AO application, very high continuous frame rates of the order of 1 kHz are required for a matrix of 512x512 pixels. The design concepts of a parallel readout board are presented that will allow this fast data throughput. The development status of the optical WFS tube is also explained

Interstellar Matter and the Boundary Conditions of the Heliosphere

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun, and determines the boundary conditions of the heliosphere. Both the Sun and interstellar clouds move through space, so these boundary conditions change with time. Data and theoretical models now support densities in the cloud surrounding the solar system of n(HI)=0.22+/-0.06 cm^-3, and n(e-)~0.1 cm-3, with larger values allowed for n(HI) by radiative transfer considerations. Ulysses and Extreme Ultraviolet Explorer satellite HeI data yield a cloud temperature of 6,400 K. Nearby interstellar gas appears to be structured and inhomogeneous. The interstellar gas in the Local Fluff cloud complex exhibits elemental abundance patterns in which refractory elements are enhanced over the depleted abundances found in cold disk gas. Within a few parsecs of the Sun, inconclusive evidence for factors of 2--5 variation in MgII and FeII gas phase abundances is found, providing evidence for variable grain destruction. Observations of the hydrogen pile-up at the nose of the heliosphere are consistent with a barely subsonic motion of the heliosphere with respect to the surrounding interstellar cloud. Uncertainties on the velocity vector of the cloud that surrounds the solar system indicate that it is uncertain as to whether the Sun and alpha Cen are or are not immersed in the same interstellar cloud.Comment: 24 pages 3 figure

Is the Sun Embedded in a Typical Interstellar Cloud?

The physical properties and kinematics of the partially ionized interstellar material near the Sun are typical of warm diffuse clouds in the solar vicinity. The interstellar magnetic field at the heliosphere and the kinematics of nearby clouds are naturally explained in terms of the S1 superbubble shell. The interstellar radiation field at the Sun appears to be harder than the field ionizing ambient diffuse gas, which may be a consequence of the low opacity of the tiny cloud surrounding the heliosphere. The spatial context of the Local Bubble is consistent with our location in the Orion spur.Comment: "From the Outer Heliosphere to the Local Bubble", held at International Space Sciences Institute, October 200

Patient-derived xenografts and organoids model therapy response in prostate cancer.

Therapy resistance and metastatic processes in prostate cancer (PCa) remain undefined, due to lack of experimental models that mimic different disease stages. We describe an androgen-dependent PCa patient-derived xenograft (PDX) model from treatment-naïve, soft tissue metastasis (PNPCa). RNA and whole-exome sequencing of the PDX tissue and organoids confirmed transcriptomic and genomic similarity to primary tumor. PNPCa harbors BRCA2 and CHD1 somatic mutations, shows an SPOP/FOXA1-like transcriptomic signature and microsatellite instability, which occurs in 3% of advanced PCa and has never been modeled in vivo. Comparison of the treatment-naïve PNPCa with additional metastatic PDXs (BM18, LAPC9), in a medium-throughput organoid screen of FDA-approved compounds, revealed differential drug sensitivities. Multikinase inhibitors (ponatinib, sunitinib, sorafenib) were broadly effective on all PDX- and patient-derived organoids from advanced cases with acquired resistance to standard-of-care compounds. This proof-of-principle study may provide a preclinical tool to screen drug responses to standard-of-care and newly identified, repurposed compounds

A cost-effective algae-based biosensor for water quality analysis: Development and testing in collaboration with peasant communities

New anthropic potentially harmful compounds are released into the environment everyday. In this context, broad range bioassays have emerged providing economically viable and widely applicable alternatives due to their ability to detect the cumulative toxicity of mixtures of both known and unknown chemicals in a sample, thus allowing direct information about water quality. Here we present a low-cost, wide-range algae-based biosensor that is easy to assemble and operate by untrained users and provides direct readings. It was developed as a request of a peasant social movement organization to assess the toxicity of drinking water in rural communities affected by pesticide spraying. Two fresh water algae strains, Scenedesmus acutus and Pseudokirchneriella subcapitata, were immobilized in alginate beads and tested as bioindicators. After incubation with different pollutants for five days, naked eye analysis by several observers proved to be a successful method to survey algae’s growth and establish the detection limits. Best detection limits were 10 ppm for technical-grade acid glyphosate, 15 ppm for glyphosate-based formulation, 50 ppb for atrazine formulation, 7.5 ppm for copper and 250 ppb for chromium. Absorbance measurements upon algae resuspension validated these results. The developed device was successfully tested in participatory workshops conducted at rural communities. Children, adults and elders with no scientific training were able to build the sensor and interpret the results, thus evaluating the quality of rain and well water used in their communities.Universidad Nacional de Santiago del EsteroConsejo Nacional de Investigaciones Científicas y Técnica