Discovery and Characterisation of Ultra-Cool Dwarfs in Large Scale Surveys

Ultracool dwarfs including the lowest mass stars and substellar dwarfs (or brown dwarfs) is a rapidly evolving and very active field. In this thesis I present the discovery and characterization of ultracool dwarfs and their binary systems with solar and subsolar abundances and try to answer a few scientific questions related to these ultracool objects. I use different techniques based on photometric and astrometric data of modern large scale surveys to identify ultracool dwarfs and their binaries. I identify around 1000 ultracool dwarfs from SDSS, 2MASS and UKIDSS surveys, including 82 L dwarfs and 129 L dwarf candidates (Chapter 2 and 4). This work largely increases the known number of ultracool dwarfs and aid the statistic study of these objects. Eighteen ultracool dwarfs in my sample are found to be in wide binary systems by common proper motion (Chapter 4 and 5). Wide binary systems are often used to test formation theories of low mass stars and brown dwarfs, which have different predictions of separations and binary fractions. One of these binary systems is the first L dwarf companion to a giant star eta Cancri. The eta Cancri B is clearly a useful benchmark object, with constrained distance, age, and metallicity. Further more, the L3.5 dwarf companion eta Cancri B is found to be a potential L4 + T4 binary. I focus on the studies of low mass stars and brown dwarfs with subsolar abundance referred as red and ultracool subdwarfs. They belong to the older Population II of the Galactic halo contain more information of the formation, early evolution and structure of the Milky Way. Using the most extensive optical survey, the Sloan Digital Sky Survey (SDSS), to select low mass stars with subsolar abundance, referred as red subdwarfs with spectral types of late K and M. I identify about 1800 M subdwarfs including 30 new >M6 subdwarfs and five M ultra subdwarfs with very high gravity as well as 14 carbon enhanced red subdwarfs. I also identify 45 red subdwarf binary systems from my red subdwarf sample. Thirty of them are in wide binary systems identified by common proper motion. Fifteen binaries are partially resolved in SDSS and UKIDSS. I estimate the M subdwarf binary fraction. I fit the relationships of spectral types and absolute magnitudes of optical and near infrared bands for M and L subdwarfs. I also measure $UVW$ space velocities of the my M subdwarf sample (Chapter 5). Our studies of the lowest mass stars and brown dwarfs of the Galactic halo are limited by the lack of known objects. There are only seven L subdwarfs published in the literature. I search for ultracool subdwarfs by a combine use of the most extensive optical and near infrared surveys, the SDSS and the UKIRT Infrared Deep Sky Survey. I identify three new L subdwarfs with spectral types of sdL3, sdL7 and esdL6. I re-examine the spectral types and metal classes of all known L subdwarfs and propose to use 2.3 um CO line as an indicator of L subdwarfs. Two of my new L subdwarfs are found to be candidates of halo brown dwarfs (or substellar subdwarfs). I find four of these known ten L subdwarfs could be halo brown dwarfs. I propose a new name "purple dwarf" for lowest-mass stars and brown dwarfs with subsolar abundance (Chapter 3). Finally I summarize and discuss the thesis project in Chapter 6 and describe future research plans in Chapter 7

Simulation of an Electromagnetic Acoustic Transducer Array by Using Analytical Method and FDTD

Previously, we developed a method based on FEM and FDTD for the study of an Electromagnetic Acoustic Transducer Array (EMAT). This paper presents a new analytical solution to the eddy current problem for the meander coil used in an EMAT, which is adapted from the classic Deeds and Dodd solution originally intended for circular coils. The analytical solution resulting from this novel adaptation exploits the large radius extrapolation and shows several advantages over the finite element method (FEM), especially in the higher frequency regime. The calculated Lorentz force density from the analytical EM solver is then coupled to the ultrasonic simulations, which exploit the finite-difference time-domain (FDTD) method to describe the propagation of ultrasound waves, in particular for Rayleigh waves. Radiation pattern obtained with Hilbert transform on time-domain waveforms is proposed to characterise the sensor in terms of its beam directivity and field distribution along the steering angle, which can produce performance parameters for an EMAT array, facilitating the optimum design of such sensors

Measuring ultracool properties from the UKIDSS Large Area Survey

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe discuss the properties and of ultracool and brown dwarfs that can be measured from current large area surveys and how fundamental parameters, such as the mass function and formation history can be measured, describing our own first measurement of the formation history in the sub-stellar regime using data from the UKIDSS Large Area Survey

The Science Advantage of a Redder Filter for WFIRST

WFIRST will be capable of providing Hubble-quality imaging performance over several thousand square degrees of the sky. The wide-area, high spatial resolution survey data from WFIRST will be unsurpassed for many decades into the future. With the current baseline design, the WFIRST filter complement will extend from the bluest wavelength allowed by the optical design to a reddest filter (F184W) that has a red cutoff at 2.0 microns. In this white paper, we outline some of the science advantages for adding a K_s filter with a 2.15 micron central wavelength in order to extend the wavelength coverage for WFIRST as far to the red as the possible given the thermal performance of the observatory and the sensitivity of the detectors

Stimulated thyroglobulin and pre-ablation antithyroglobulin antibody products can predict the response to radioiodine therapy of TgAb-positive differentiated thyroid cancer patients: a retrospective study

ObjectiveWe aimed to explore the predictive value of stimulated thyroglobulin (sTg) and pre-ablation antithyroglobulin (pa-TgAb) products for the effect of radioiodine therapy (RAIT) on TgAb-positive differentiated thyroid cancer (DTC) patients.MethodsIn this study, we enrolled 265 patients with TgAb-positive DTC who underwent RAIT after total thyroidectomy (TT). Based on the last follow-up result, the patients were divided into two groups: the excellent response (ER) group and the non-excellent response (NER) group. We analyzed the factors related to the effect of RAIT.ResultsThe ER group consisted of 197 patients. The NER group consisted of 68 patients. For the univariate analysis, we found that the maximal tumor diameter, whether with extrathyroidal extension (ETE), bilateral or unilateral primary lesion, multifocality, preoperative TgAb (preop-TgAb), pa-TgAb, sTg × pa-TgAb, initial RAIT dose, N stage, and surgical extent (modified radical neck dissection or not), showed significant differences between the ER group and NER group (all p-values <0.05). The receiver operating characteristic (ROC) curves showed that the cutoff value was 724.25 IU/ml, 424.00 IU/ml, and 59.73 for preop-TgAb, pa-TgAb, and sTg × pa-TgAb, respectively. The multivariate logistic regression analysis results indicated that pa-TgAb, sTg × pa-TgAb, initial RAIT dose, and N stage were independent risk factors for NER (all p-values <0.05). For the Kaplan–Meier analysis of disease-free survival (DFS), the median DFS of the patients with sTg × pa-TgAb < 59.73 and initial RAIT dose ≤ 100 mCi was significantly longer than that of the patients with sTg × pa-TgAb ≥ 59.73 (50.27 months vs. 48.59 months, p = 0.041) and initial RAIT dose >100 mCi (50.50 months vs. 38.00 months, p = 0.030).ConclusionWe found the sTg and pa-TgAb conducts is a good predictor of the efficacy of RAIT in TgAb-positive DTC patients. It can play a very positive and important role in optimizing treatment, improving prognosis, and reducing the burden of patients

The Science Advantage of a Redder Filter for WFIRST

WFIRST will be capable of providing Hubble-quality imaging performance over several thousand square degrees of the sky. The wide-area, high spatial resolution survey data from WFIRST will be unsurpassed for many decades into the future. With the current baseline design, the WFIRST filter complement will extend from the bluest wavelength allowed by the optical design to a reddest filter (F184W) that has a red cutoff at 2.0 microns. In this white paper, we outline some of the science advantages for adding a K_s filter with a 2.15 micron central wavelength in order to extend the wavelength coverage for WFIRST as far to the red as the possible given the thermal performance of the observatory and the sensitivity of the detectors

Primeval very low-mass stars and brown dwarfs – VII. The discovery of the first wide M + L extreme subdwarf binary

International audienc

Cancerous Inhibitor of PP2A Silencing Inhibits Proliferation and Promotes Apoptosis in Human Multiple Myeloma Cells

Multiple myeloma is the second most prevalent type of blood cancer, representing approximately 1% of all cancers and 2% of all cancer deaths. There is therefore a strong need to identify critical targets in multiple myeloma neoplasia and progression. Cancerous inhibitor of PP2A (CIP2A) is a human oncoprotein that regulates cancer cell viability and anchorage-independent growth and induces apoptosis. The present study investigated CIP2A function in the human multiple myeloma cell lines RPMI-8226 and NCI-H929 to determine whether it can serve as a potential therapeutic target. CIP2A was silenced in the cells by transfection of short interfering RNA and cell proliferation and apoptosis were evaluated by a tetrazolium salt-based assay and flow cytometry, respectively. CIP2A knockdown inhibited proliferation and induced apoptosis in RPMI-8226 and NCI-H929 cells and decreased the phosphorylation of phosphoinositide 3-kinase (PI3K) p85, AKT1, and mammalian target of rapamycin (mTOR) without affecting total protein levels. Treatment of CIP2A-depletion cells with insulin-like growth factor 1 decreased the effects of CIP2A inhibition on cell viability and apoptosis. These results indicate that CIP2A modulates myeloma cell proliferation and apoptosis via PI3K/AKT/mTOR signaling and suggest that it can potentially serve as a drug target for the treatment of multiple myeloma