Research in Biomedical Imaging
Research in Biomedical Imaging
Current projects
Increasing the depth-of-field in a system based on Optical Projection Tomograph
Collaborators: R. Mark Henkelman, Jun Dazai
Description
The OPT is a new microscopic imaging technique developed by Dr. J. Sharpe in 2002. It offers significant advantages over other 3D imaging modalities (e.g. magnetic resonance imaging (MRI), confocal microscopy CT etc.) in the studies of gene expression and development. First, it provides high resolution, on the order of microns to tens of microns, i.e. celullar resolution. Secondly, it is also able to cover large specimens (~ 1 cm^3) using both absorbing and fluorescent molecular markers, thus extending the imaging capabilities to small animals.
The goal of my work is to improve the depth of field on the OPT, while keeping the resolution the same. This would make the OPT able to image larger specimens at high resolution and provide a 3D reconstruction of shapes for even more developed embryos. So more biology can be seen.
Research in Astronomy
Current projects
Ultra-Luminous Globular Clusters and Ultra-Compact Dwarf Galaxies in the Virgo Cluster
Collaborators: P. Côté, S.G. Djorgovski, D. McLaughlin, and the ACS Virgo Cluster Survey Team: J. Blakeslee, L. Ferrarese, A. Jordán, S. Mei, D. Merritt, M. Milosavljevic, E. Peng, J. Tonry, M.J. West.
Facilities: For spectroscopy -- Keck II and the Echellette Spectrograph and Imager (ESI); For imaging -- HST and the Advance Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2).
Status: Results published in Hasegan et al. 2005, and Hasegan et al. 2009 in preparation.
Summary: We have examined the dynamics and kinematics of compact, high-luminosity globular cluster candidates associated with M87 and other early-type galaxies in the Virgo Cluster. Among these objects, we found ``normal'' globular clusters which follow the scaling relations of their Galactic counterparts, as well as larger and more massive "ultra-compact dwarfs" which resemble the nuclei of nucleated dwarf elliptical galaxies and may contain dark matter. One additional object may be an old "stellar supercluster", formed through the amalgamation of multiple young massive clusters.
Internal Dynamics and Kinematics of Virgo Dwarf Elliptical Galaxies
Collaborators: P. Côté and the ACS Virgo Cluster Survey Team.
Facilities: Keck/ESI, HST/ACS and HST/WFPC2.
Status: In progress.
Description
Dwarf elliptical galaxies are the most common type by number in the Local Universe, yet we know very little about their properties and origin. Likewise, nucleated dwarf elliptical galaxies make up a large fraction of the dwarf galaxy population in rich clusters such as Virgo, but relatively little kinematic data exist for this class of object since the Local Group contains only one such example (NGC205). Their distinguishing feature is a bright, compact nucleus whose origins have been debated for many years. In addition, it is not clear whether the nucleated and nonnucleated dwarfs share a common formation and evolution differing only on their typical luminosity, or are separated by more profound differences (e.g. morphological structure, stellar populations).
An improved understanding of their dynamical correlations will provide important constraints on their formation mechanism. For example, in hierarchical formation models, the dEs form out of small density fluctuations in the early Universe and so they should be flattened by velocity anisotropy. In contrast, in the galaxy harrasment scenario, dE's progenitor is a spiral or irregular galaxy transformed by the cluster environment and a significant fraction of the progenitor's rotation can be preserved. Observing dEs, however, has been extremely difficult due to their low-luminosity and/or low-surface brightness. Only Local Group dEs and few Virgo and Fornax Cluster dEs.
To shed light on these issues, we study faint Virgo Cluster dEs, some of them presenting a nucleus. We will derive kinematical and dynamical properties for these dEs and also for the nuclei of the nucleated dEs.
Past projects
Magnetic Monopole Detection
Massive magnetic monopoles are predicted by most Grand Unified Theories (GUTs). They should have been produced in the very early universe and should still exist as cosmic relicts today. A lot of experiments (Baksan, Ohya, MACRO) have been trying to detect them in the penetrating cosmic radiation.
Since the passage of heavily ionizing particles may be recorded in insulating materials, we estimated the acceptance of a possible large area (1000 m2) monopole detector, located at the Earth's surface. The condition of detectability was studied for the CR-39 detector used by the MACRO experiment at Gran Sasso. We (Hasegan & Popa 1998) assumed an isotropic (outside the Earth) monopole flux, with different magnetic charges and we took into consideration the absorbtion in the Earth (for up-going monopoles). Our calculations indicate that a sensitivity of the order of few 10-17cm-2s-1sr-1 could be reached by such experiment in a reasonable number of years.
Study on Cosmic Microwave Background (CMB) Radiation Anisotropies
We (Hasegan, Popa & Stefanescu 1998) performed a comparison between the CMB anisotropy data obtained with two different instruments of the COsmic Background Explorer (COBE): the Far Infrared Absolute Spectrophotometer (FIRAS) and Differential Microwave Radiometers (DMR). Using the FIRAS data, we determined the CMB spectrum, the dipolar anisotropy and the spectrum of the Galactic emission, while from the second one, we measured the CMB temperature anisotropy.