22,351 research outputs found
Spectral analysis of the Chandra comet survey
No full textAims.We present results of the analysis of cometary X-ray spectra with an extended version of our charge exchange emission model (Bodewits et al. 2006). We have applied this model to the sample of 8 comets thus far observed with the Chandra X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1 (LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005 (Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include a broad variety of comets, solar wind environments and observational conditions. Methods.The interaction model is based on state selective, velocity dependent charge exchange cross sections and is used to explore how cometary X-ray emission depend on cometary, observational and solar wind characteristics. It is further demonstrated that cometary X-ray spectra mainly reflect the state of the local solar wind. The current sample of Chandra observations was fit using the constrains of the charge exchange model, and relative solar wind abundances were derived from the X-ray spectra. Results.Our analysis showed that spectral differences can be ascribed to different solar wind states, as such identifying comets interacting with (I) fast, cold wind, (II), slow, warm wind and (III) disturbed, fast, hot winds associated with interplanetary coronal mass ejections. We furthermore predict the existence of a fourth spectral class, associated with the cool, fast high latitude wind
A star-forming galaxy at z= 5.78 in the Chandra Deep Field South
No full textWe report the discovery of a luminous z = 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ‘i-drop’ from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (i′−z′)AB = 1.6 indicated a spectral break consistent with the Lyman α forest absorption shortward of Lyman α at z≈ 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so rhl 5. Our spectroscopic redshift for this object confirms the validity of the i′-drop technique of Stanway et al. to select star-forming galaxies atz≈ 6
Negatively supercharging cellulases render them lignin-resistant
No full textNon-specific adsorption of cellulases to lignin hinders enzymatic deconstruction of lignocellulosic biomass. Here we tested the hypothesis that negatively supercharging cellulases could reduce lignin inhibition. Computational design was used to negatively supercharge the surfaces of Ruminoclostridium thermocellum family 5 CelE and a CelE-family 3a carbohydrate binding module fusion. Resulting designs maintained the same expression yield, thermal stability, and nearly identical activity on soluble substrate as the wild-type proteins. Four designs showed complete lack of inhibition by lignin but with lower cellulose conversion compared to original enzymes. Increasing salt concentrations could partially rescue the activity of supercharged enzymes, supporting a mechanism of electrostatic repulsion between designs and cellulose. Results showcase a protein engineering strategy to construct highly active cellulases that are resistant to lignin-mediated inactivation, although further work is needed to understand the relationship between negative protein surface potential and activity on insoluble polysaccharides.Peer reviewe
Multipurpose small area estimation
No full textSample surveys are generally multivariate, in the sense that they measure more than oneresponse variable. In theory, each variable can then be assigned an optimal weight forestimation purposes. However, it is often a distinct practical advantage to have a singleweight that is used with all variables collected in the survey. This paper describes howsuch multipurpose sample weights can be constructed when small area estimates of thesurvey variables are required. The approach is based on the model-based direct (MBD)method of small area estimation described in Chambers and Chandra (2006). Empiricalresults reported in this paper show that MBD estimators for small areas based onmultipurpose weights perform well across a range of variables that are often of interest inbusiness surveys. Furthermore, these results show that the proposed approach is robust tomodel misspecification and also efficient for the variables ill-suited to standard methodsof small area estimation (e.g. variables that contain a significant proportion of zeros).<br/
MIROC4-ACTM CO2 Inversion flux (2001-2022)
No full text<p>This dataset is prepared for GCP CO2-2023 assessment. </p>
<p>Inversion Details are in:</p>
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<div>Chandra, N., Patra, P. K., Niwa, Y., Ito, A., Iida, Y., Goto, D., Morimoto, S., Kondo, M., Takigawa, M., Hajima, T., and Watanabe, M.: Estimated regional CO<sub>2</sub> flux and uncertainty based on an ensemble of atmospheric CO<sub>2</sub> inversions, Atmos. Chem. Phys., 22, 9215–9243, https://doi.org/10.5194/acp-22-9215-2022, 2022</div>
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<div>MIROC4-ACTM Details:</div>
<div><span>Patra, P. K., Takigawa, M., Watanabe, S., Chandra, N., Ishijima, K., and Yamashita, Y.: Improved Chemical Tracer Simulation by MIROC4.0-based Atmospheric Chemistry-Transport Model (MIROC4-ACTM), SOLA, 14, 91–96, <a href="https://doi.org/10.2151/sola.2018-016">https://doi.org/10.2151/sola.2018-016</a>, 2018. </span></div>
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Compact objects in active galactic nuclei and X-ray binaries
No full textIn this thesis I study the inner-most regions of Active Galactic Nuclei (AGN) using
the reverberation mapping technique, and neutron star low-mass X-ray binaries in
quiescence using X-ray observations.
Using the 13-year optical monitoring data for the AGN NGC 5548, the luminosity dependence
of the Hβ emitting radius was modelled using a delay map, finding that
the radius scales with luminosity as predicted by recent theoretical models. Time-delays
between the continuum at different wavelengths in AGN can be used to probe the accretion
disc. Here, continuum time-delays in a sample of 14 AGN were used to measure the radial
temperature profile of the accretion discs, determine the nuclear extinction, and measure
distances to the objects. However, the distances measured correspond to a value for
Hubble's constant that is a factor of ~2 lower than the accepted value. The implications
of this on the thermal disc reprocessing model are discussed.
I present two Chandra observations of the neutron star transient in the globular
cluster NGC 6440 in quiescence, where the power-law component to the spectrum is seen
to be variable between the observations, suggesting that there is ongoing residual accretion.
From a Chandra observation of the globular cluster Terzan 1, I have identifed the likely
quiescent counterpart to a transient previously observed in outburst, and discuss the other
sources within the cluster. Using Chandra and XMM-Newton monitoring observations of
two neutron star transients (KS 1731-260 and MXB 1659-29) in quiescence I have found
that the neutron star crusts in both sources have now returned to thermal equilibrium
with the core. These observations also indicate that the crusts in both sources may have
a high thermal conductivity and that enhanced neutrino emission may be occurring in the
core. Finally, the discovery of an X-ray transient with XMM-Newton is presented, and the
other sources in this observation discussed
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