Natural Sciences
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Zhefu Yu
Postdoctoral Scholar, Physics
Current Research and Scholarly InterestsMy research aims to understand how supermassive black holes (SMBHs) grow over cosmic time, one of the key questions in astrophysics.
I have done substantial work in accurately measuring the mass of SMBHs through reverberation mapping (RM). In particular, I derived a new relationship between the radius of the Mg II broad line region and the continuum luminosity of the active galactic nuclei (AGN) based on the OzDES RM project, which is critical for SMBH mass measurements and demographic studies in cosmic noon – the peak of AGN activity. I have also done extensive work in understanding the accretion physics in both AGN and quiescent SMBHs.
Now my work focuses on better understanding the accretion onto SMBHs, the major path of SMBH growth. I collaborate closely with the XOC group and the Rubin LSST team in KIPAC. My research probes the inner most region of the AGN accretion disk through joint analysis of the X-ray spectral and timing data. I will also probe the accretion disk through time domain analysis of the LSST data in the near future. -
Richard Zare
Marguerite Blake Wilbur Professor of Natural Science and Professor, by courtesy, of Physics
Current Research and Scholarly InterestsMy research group is exploring a variety of topics that range from the basic understanding of chemical reaction dynamics to the nature of the chemical contents of single cells.
Under thermal conditions nature seems to hide the details of how elementary reactions occur through a series of averages over reagent velocity, internal energy, impact parameter, and orientation. To discover the effects of these variables on reactivity, it is necessary to carry out studies of chemical reactions far from equilibrium in which the states of the reactants are more sharply restricted and can be varied in a controlled manner. My research group is attempting to meet this tough experimental challenge through a number of laser techniques that prepare reactants in specific quantum states and probe the quantum state distributions of the resulting products. It is our belief that such state-to-state information gives the deepest insight into the forces that operate in the breaking of old bonds and the making of new ones.
Space does not permit a full description of these projects, and I earnestly invite correspondence. The following examples are representative:
The simplest of all neutral bimolecular reactions is the exchange reaction H H2 -> H2 H. We are studying this system and various isotopic cousins using a tunable UV laser pulse to photodissociate HBr (DBr) and hence create fast H (D) atoms of known translational energy in the presence of H2 and/or D2 and using a laser multiphoton ionization time-of-flight mass spectrometer to detect the nascent molecular products in a quantum-state-specific manner by means of an imaging technique. It is expected that these product state distributions will provide a key test of the adequacy of various advanced theoretical schemes for modeling this reaction.
Analytical efforts involve the use of capillary zone electrophoresis, two-step laser desorption laser multiphoton ionization mass spectrometry, cavity ring-down spectroscopy, and Hadamard transform time-of-flight mass spectrometry. We believe these methods can revolutionize trace analysis, particularly of biomolecules in cells.
