Welcome to Ruxandra Bondarescu's Page!



Welcome to my page. I received my PhD in physics in August 2008 from Cornell University and I am now a postdoc at Penn State. I work with Sam Finn on recovering waveforms from LIGO data through a "maximum entropy" method that cross-correlates data at different detectors. This is particularly useful for searches in which we do not have a template for the gravitational wave signal. Additionaly, it is faster than matched filtering and could also be used to narrow the search to templates that are correlated with the data.

Other Topics I work on include

  • Rmodes in neutron stars. Rmodes are oscillations that occur in rotating fluids. In rapidly rotating neutron stars these modes can be unstable. The instability is driven by the gravitational radiation reaction. The most relvant mode for gravitational radiation emisson is the Rossby wave with L=m=2. This mode is unstable when gravitational driving dominates viscous dissipation. I model the nonlinear interactions between the L=m=2 r-mode and other near-resonant modes in the star. The r-mode instability provides a limiting frequency for accreting neutron stars explaining why we have not seen submillisecond pulsars. Gravitational wave emission from r-modes can also spin down newborn neutron star in the first few years after formation closer to the observed periods of young pulsars. My PhD advisors Ira Wasserman and Saul Teukolsky and I worked on both r-modes in acreeting neutron stars and newborn pulsars.

  • Beams and mirror shapes for future gravitational wave interferometers. I worked on lowering thermal noise in gravitational wave detectors by reshaping mirrors and hence increasing the event rate for gravitational wave detection. We found that finite mirror effects are important and result in a preferred beam width for Mesa and hyperboloidal beams in advanced LIGO. We have shown that thermal noise can be reduced by 12% with no additional effort by using finite mirror effects to our advantage rather then working against them and by 28% with some modifications to the mirror to match the phase i front of the finite beam rather than that of the infinite beam. This work is in collaboration with Andy Lundgren (Syracuse U.) and Dave Tsang (Cornell) and my brother, Mihai Bondarescu (AEI/Caltech/U. of Mississippi). We are now extending this work to conical mirrors, which were found to be optimal for minimizing thermal noise [in Mihai's Caltech PhD thesis].

  • Exotic Dark Matter Candidates. About 22% of the matter in the universe is estimated to be non-baryonic. Light axions could have been created by non-thermal processes in the early universe leaving them slow moving and compatible with preferred cold-dark matter models. Stars composed of such particles would be an exotic source of gravitational waves. Their detection would confirm the presence of scalar field dark matter. We studied propreties of these stars using a 3D code based on the Cactus Computational Toolkit (www.cactuscode.org), their stability under spherical and non-spherical perturbations and the gravitational waveforms they produce. We focused on both boson stars (complex scalar field configurations) and soliton stars (real scalar field). This work has been done in collaboration with Jayashree Balakrishna (Harris Stowe University), Gregory Daues (NCSA), Francisco S. Guzman (Universidad Michoacana de San Nicolas de Hidalgo, Mexico), Mihai Bondarescu (AEI/Caltech/U. of Mississippi), and Ed Seidel (LSU/CCT).
    • Contact Info: ruxandrab7ATgmail.com
    334 Whitmore Lab, State College, PA
    Projects I am working on
    Note: This is the research statement I used to apply for postdocs. Has not been updated since fall 2007.
    CV pdf [2007 version]
    Personal my Family My brother's page Pictures and fun

    Publications

    Work in Progress

    A. Lundgren, R. Bondarescu , D. Tsang, and M. Bondarescu, "Optimal mirrors and beam shapes for Advanced LIGO"

    Refereed Publications

    6. R. Bondarescu, S. Teukolsky, and I. Wasserman,
    "Spinning Down Newborn Neutron Stars: Nonlinear Development of the R-mode Instability",
    arXiv:0809.3448 Submitted to Phys. Rev. D

    5. A. Lundgren, R. Bondarescu , D. Tsang, M. Bondarescu,
    "Finite Mirror Effects in Advanced Interferometric Gravitational Wave Detectors",
    arxiv:0710.3808, Phys. Rev. D 77, 042003 (2008).

    4. J. Balakrishna, R. Bondarescu , G. Daues, M. Bondarescu,
    "Numerical Simulations of Oscillating Soliton Stars: Excited States in Spherical Symmetry and Ground State Evolutions in 3D",
    arxiv:0710.4131, Phys. Rev. D 77, 024028 (2008).

    3. R. Bondarescu, S. Teukolsky, and I. Wasserman,
    "Spin Evolution of Accreting Neutron Stars: Nonlinear Development of the R-mode Instability",
    arXiv:0704.0799, Phys. Rev. D 76, 064019 (2007).

    2. J. Balakrishna, R. Bondarescu, G. Daues, F. Guzman, and E. Seidel,
    "Evolution of 3D Boson Stars with Waveform Extraction",
    Class. Quantum Grav. 23 (2006) 2631-2652, gr-qc/0602078.

    1. R. Bondarescu, G. Allen, G. Daues, I. Kelley, M. Russell, E. Seidel, J. Shalf, M. Tobias,
    "The Astrophysics Simulation Collaboratory Portal: a Framework for Effective Distributed Research",
    Future Generation Computing Systems 21 (2005) 259-270, Special Issue on Advanced Grid Technologies.
    PDF version of the paper   Abstract through Science Direct

    Ph.D. Thesis Ruxandra Bondarescu, Cornell University, August 2008.

    Conferences and Talks

    Physics Talks
    1. "Rossby waves in neutron stars", CAM 2007, Montreal, Canada, August 2007, (Travel Grant from APS)
    2. "Spin Evolution of Accreting Neutron Stars and the R-mode Instability", GR18, Australia, July 2007 (ICPS travel grant + Cornell Travel Grant + NSF travel grant).
    3. "Spin Evolution of Accreting Neutron Stars: Nonlinear Effects of the R-mode Instability", East Coast Gravity Meeting and The Teukolsky Birthday Symposium, Cornell, June 2007 (free; I also chaired a session ).
    4. "Spin Evolution of Neutron Stars: Nonlinear Effects of the R-mode Instability", April APS Meeting, Florida, 2007 (Travel Grant from both Cornell and APS)
    5. "R-modes in Spinning neutron stars", International Conference for Physics Students, Bucharest, Romania, August 2006.
    6. "How fast can neutron stars spin?", CAM 2005 (Travel grant awarded by APS that covered all expenses)
    7. "Evolution of 3D boson stars", April APS Meeting 2004, Tampa, Florida (Travel grant awarded by APS to attend this conference)
    8. "Boson Stars", East Coast Gravity Meeting, March 2003
    9. "Introduction to Boson Stars", West University of Timisoara (invited talk)


    Old computer science talks
    1. "Requirements for Grid Enabling an Application", presented at the GAT Workshop, Cardiff University, United Kingdom, July 2003 Slides
    2. "The Astrophysics Simulation Collaboratory Portal", presented at the GridLab All Hands conference and workshop, Eger, Hungary, April 2003 Powerpoint Slides
    3. "The ASC Portal: A Tool for Numerical Relativity", presented at Louisiana State University, February, 2003
    4. "Grid and Portal Technology Tutorial", presented at West University of Timisoara, Romania, March, 2003
    5. "Short overview of research activities at the LSU CAPITAL + Short Cactus Tutorial", presented as part of the Gravitational Waves Fun - Louisiana State University, January, 2004 (Slides)

    Teaching and TAing

    • Cornell University
      Physics 217 - Electricity and Magnetism for Honor Students: Spring 2005 (part time TA) with Prof. Lois Pollack, Fall 2005 (full time TA) with Prof. Andre Leclair
    • My brother and I organized a series of 14 Gravitational Waves lectures at LSU (December 03-January 04) based on Kip Thorne's Ph. 237. We received funding from LSU CAPITAL to organize the lectures. I organized the last 4 lectures after Mihai left with help from Greg. We did the same thing at Cornell in the Spring of 2004 (and for part of the summer) and here I was the main organizer.
      Gravitational Waves Fun at Cornell - Spring 2004
      Gravitational Waves Fun at LSU - Winter 2003
    • Department of Physics, University of Illinois at Urbana-Champaign, IL
      1. Teaching Assistant
        Course: Physics 371 (Advanced Optics- Light)
        Professor: Taekjip Ha
        Spring 2003
      2. Teaching Assistant
        Course: Physics 140 (Practical Physics: How Things Work)
        Professor: Laura H. Greene
        Fall 2002
      3. Teaching Assistant
        Course: Physics 114 (General Physics: Waves and Quantum Mechanics)
        Professor: Gary Gladding and Lance Cooper
        Spring 2002



    These are two webpages with pics from boson star simulations. They were primarly written to convince my undergraduate advisor that we had enough for a paper and it worked :).

    Boson Star Results (Last Updated Jan 25, 2004)

    Older Webpage with Results (Last Updated Dec 1, 2003)