68 research outputs found
Characterising the gas and dust in protoplanetary discs around Herbig stars
This thesis contains a study of the circumstellar discs around intermediate
mass stars. Through observational data and protoplanetary
disc modelling, the physical structure and composition of protoplanetary
discs are investigated with regards to their capacity for planet
formation.
In-depth analysis of millimetre-wavelength interferometric observations
are carried out on the circumstellar environment of two Herbig
stars. Firstly, the distribution of gas and dust in the gas-rich, potentially
planet-hosting disc of HD100546 is characterised. Using ALMA
observations of 1.3mm continuum and CO isotopologues tracing the
disc midplane, estimates of disc mass are calculated, constraints on
the size of dust grains inferred and evidence for midplane counterparts
to scattered light features are identified.
Secondly, an analysis of the more evolved circumstellar disc around
Herbig star HD141569 is made in order to investigate the mass content
of the disc and inform the debate as to its evolutionary stage.
New ALMA observations presented in this thesis and new midplane
structures in the gas and dust that support an intermediary stage of
evolution between the protoplanetary disc and debris disc regimes.
Finally, modelling of the pre-main sequence evolution of stars across
the stellar mass range at which exoplanet detections peak is combined
with Monte Carlo radiative transfer and modelling of the evolution of
midplane gas and dust in order to study the impact of stellar evolution
on the midplanes of protoplanetary discs. Variations in midplane
temperature profles result in different locations of key snowlines in the
disc, which in turn produces variations in the molecular composition
of the local disc. The results quantify how snowline locations depend
on stellar luminosity evolution. This modelling procedure is applied
to the system of HR8799 in order to put constraints on the time and
location within the disc at which wide-orbit planets could have formed
based on their atmospheric C/O ratio. The results support an early
formation time, within around 1 Myr, for the carbon-rich exoplanet
HR8799b
A Candidate Brightest Proto-Cluster Galaxy at z = 3.03
We report the discovery of a very bright (m_R = 22.2) Lyman break galaxy at z
= 3.03 that appears to be a massive system in a late stage of merging. Deep
imaging reveals multiple peaks in the brightness profile with angular
separations of ~0.''8 (~25 h^-1 kpc comoving). In addition, high
signal-to-noise ratio rest-frame UV spectroscopy shows evidence for ~5
components based on stellar photospheric and ISM absorption lines with a
velocity dispersion of sigma ~460 km s^-1 for the three strongest components.
Both the dynamics and high luminosity, as well as our analysis of a LCDM
numerical simulation, suggest a very massive system with halo mass M ~ 10^13
M_solar. The simulation finds that all halos at z = 3 of this mass contain
sub-halos in agreement with the properties of these observed components and
that such systems typically evolve into M ~ 10^14 M_solar halos in groups and
clusters by z = 0. This discovery provides a rare opportunity to study the
properties and individual components of z ~ 3 systems that are likely to be the
progenitors to brightest cluster galaxies.Comment: 14 pages, 3 figures, submitted to ApJ Letter
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Current Conditions Risk Assessment for the 300-FF-5 Groundwater Operable Unit
This report updates a baseline risk assessment for the 300 Area prepared in 1994. The update includes consideration of changes in contaminants of interest and in the environment that have occurred during the period of interim remedial action, i.e., 1996 to the present, as well as the sub-regions, for which no initial risk assessments have been conducted. In 1996, a record of decision (ROD) stipulated interim remedial action for groundwater affected by releases from 300 Area sources, as follows: (a) continued monitoring of groundwater that is contaminated above health-based levels to ensure that concentrations continue to decrease, and (b) institutional controls to ensure that groundwater use is restricted to prevent unacceptable exposure to groundwater contamination. In 2000, the groundwater beneath the two outlying sub-regions was added to the operable unit. In 2001, the first 5-year review of the ROD found that the interim remedy and remedial action objectives were still appropriate, although the review called for additional characterization activities. This report includes a current conditions baseline ecological and human health risk assessment using maximum concentrations in the environmental media of the 300-FF-5 Operable Unit and downstream conditions at the City of Richland, Washington. The scope for this assessment includes only current measured environmental concentrations and current use scenarios. Future environmental concentrations and future land uses are not considered in this assessment
The host galaxies and black-hole:galaxy mass ratios of luminous quasars at z~4
We present and analyse the deepest, high-quality Ks-band images ever obtained
of luminous quasars at z~4, in an attempt to determine the basic properties of
their host galaxies less than 1 Gyr after the first recorded appearance of
black holes with Mbh > 10^9 Msol. To maximise the robustness of our results we
have carefully selected two SDSS quasars at z~4. These quasars are
representative of the most luminous quasars known at this epoch but they also,
crucially, lie within 40 arcsec of comparably-bright foreground stars (required
for accurate PSF definition), and have redshifts which ensure line-free Ks-band
imaging. The data were obtained in excellent seeing (<0.4-arcsec) at the ESO
VLT with integration times of ~5.5 hours per source. Via carefully-controlled
separation of host-galaxy and nuclear light, we estimate the luminosities and
stellar masses of the host galaxies, and set constraints on their half-light
radii. The quasar host galaxies have K-band luminosities similar to radio
galaxies at comparable redshifts, suggesting that these quasar hosts are also
among the most massive galaxies in existence at this epoch. However, the quasar
hosts are a factor ~5 smaller than the host galaxies of luminous low-redshift
quasars. We estimate the stellar masses of the z~4 host galaxies to lie in the
range 2-10x10^11 Msol, and use the CIV emission line in the Sloan spectra to
estimate the masses of their black holes. The results imply a
black-hole:host-galaxy mass ratio Mbh:Mgal~0.01-0.05. This is an order of
magnitude higher than typically seen in the low-redshift Universe, and is
consistent with existing evidence for a systematic growth in this mass ratio
with increasing redshift, at least for objects selected as powerful AGN.Comment: 10 pages, 6 figure
Discovery of Macrocyclic Pyrimidines as MerTK-Specific Inhibitors
Macrocycles have attracted significant attention in drug discovery recently. In fact, a few deβ
novo designed macrocyclic kinase inhibitors are currently in clinical trials with good potency and selectivity for their intended target. In this study, we successfully engaged a structure-based drug design approach to discover macrocyclic pyrimidines as potent Mer tyrosine kinase (MerTK)-specific inhibitors. An enzyme-linked immunosorbent assay (ELISA) in 384-well format was employed to evaluate the inhibitory activity of macrocycles in a cell-based assay assessing tyrosine phosphorylation of MerTK. Through structure-activity relationship (SAR) studies, analogue 11 [UNC2541; (S)-7-amino-N-(4-fluorobenzyl)-8-oxo-2,9,16-triaza-1(2,4)-pyrimidinacyclohexadecaphane-1-carboxamide] was identified as a potent and MerTK-specific inhibitor that exhibits sub-micromolar inhibitory activity in the cell-based ELISA. In addition, an X-ray structure of MerTK protein in complex with 11 was resolved to show that these macrocycles bind in the MerTK ATP pocket
Reactivation of Kaposi's sarcoma-associated herpesvirus by natural products from Kaposi's sarcoma endemic regions
Kaposiβs sarcoma (KS) and its causative agent, Kaposiβs sarcoma associated herpesvirus (KSHV/HHV-8), a gamma2 herpesvirus, have distinctive geographical distributions that are largely unexplained. We propose the βoncoweedβ hypothesis to explain these differences, namely that environmental cofactors present in KS endemic regions cause frequent reactivation of KSHV in infected subjects, leading to increased viral shedding and transmission leading to increased prevalence of KSHV infection as well as high viral load levels and antibody titers. Reactivation also plays a role in the pathogenesis of KSHV-associated malignancies. To test this hypothesis, we employed an in vitro KSHV reactivation assay that measured increases in KSHV viral load in KSHV infected primary effusion lymphoma (PEL) cells and screened aqueous natural product extracts from KS endemic regions. Of 4,842 extracts from 38 countries, 184 (5%) caused KSHV reactivation. Extracts that caused reactivation came from a wide variety of plant families, and extracts from Africa, where KSHV is highly prevalent, caused the greatest level of reactivation. Time course experiments were performed using 28 extracts that caused the highest levels of reactivation. The specificity of the effects on viral replication was examined using transcriptional profiling of all viral mRNAs. The array data indicated that the natural extracts caused an ordered cascade of lytic replication similar to that seen after induction with synthetic activators. These in vitro data provide support for the βoncoweedβ hypothesis by demonstrating basic biological plausibility
Natural micropolymorphism in human leukocyte antigens provides a basis for genetic control of antigen recognition
Human leukocyte antigen (HLA) gene polymorphism plays a critical role in protective immunity, disease susceptibility, autoimmunity, and drug hypersensitivity, yet the basis of how HLA polymorphism influences T cell receptor (TCR) recognition is unclear. We examined how a natural micropolymorphism in HLA-B44, an important and large HLA allelic family, affected antigen recognition. T cellβmediated immunity to an Epstein-Barr virus determinant (EENLLDFVRF) is enhanced when HLA-B*4405 was the presenting allotype compared with HLA-B*4402 or HLA-B*4403, each of which differ by just one amino acid. The micropolymorphism in these HLA-B44 allotypes altered the mode of binding and dynamics of the bound viral epitope. The structure of the TCRβHLA-B*4405EENLLDFVRF complex revealed that peptide flexibility was a critical parameter in enabling preferential engagement with HLA-B*4405 in comparison to HLA-B*4402/03. Accordingly, major histocompatibility complex (MHC) polymorphism can alter the dynamics of the peptide-MHC landscape, resulting in fine-tuning of T cell responses between closely related allotypes
Mutation-Specific RAS Oncogenicity Explains NRAS Codon 61 Selection in Melanoma
N-RAS mutation at codon 12, 13 or 61 is associated with transformation; yet, in melanoma, such alterations are nearly exclusive to codon 61. Here, we compared the melanoma susceptibility of an N-RasQ61R knock-in allele to similarly designed K-RasG12D and N-RasG12D alleles. With concomitant p16INK4a inactivation, K-RasG12D or N-RasQ61R expression efficiently promoted melanoma in vivo, whereas N-RasG12D did not. Additionally, N-RasQ61R mutation potently cooperated with Lkb1/Stk11 loss to induce highly metastatic disease. Functional comparisons of N-RasQ61R and N-RasG12D revealed little difference in the ability of these proteins to engage PI3K or RAF. Instead, N-RasQ61R showed enhanced nucleotide binding, decreased intrinsic GTPase activity and increased stability when compared to N-RasG12D. This work identifies a faithful model of human N-RAS mutant melanoma, and suggests that the increased melanomagenecity of N-RasQ61R over N-RasG12D is due to heightened abundance of the active, GTP-bound form rather than differences in the engagement of downstream effector pathways
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