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Padraic Finnerty - Particle Astrophysics Graduate Student
Current Research
Experimental Particle Astrophysics
I am currently involved in research with the Experimental Nuclear and Particle Astrophysics Group at UNC. The group
collaborates on experiments involving solar neutrinos (LENS and DEAP/CLEAN), neutrinoless double beta decay
(MAJORANA), direct dark matter searches (DEAP/CLEAN), and nuclear reactions of astrophysical interest (LENA).
We are also commissioning a series of low-background counting facilities at the Kimballton mine in Virginia and
the Laboratori Nazionali del Gran Sasso (LNGS) in Italy,
in collaboration with scientists from
Virginia Tech
and NIST.
The group members are affiliated with
the
UNC Department of Physics & Astronomy and
Triangle Universities Nuclear Laboratory.
Activities of the group are supported by the
National Science Foundation (Grant #0705014), the
U.S. Department of Energy and the state of North Carolina.
I am a member of the Majorana collaboration, which aims to detect neutrinoless double beta decay in germanium-76.
My thesis project is a R&D project for Majorana. It is focused on direct dark matter detection with low-threshold high-purity germanium detectors.
The experiment is based in the Kimballton mine, located 30 minutes from the campus of Virginia Tech.
Please visit the
UNC Experimental Nuclear and Particle Astrophysics group's website for more details.
Past Research
Extrasolar Planet Hunting...
I have done research with
Dr. Jian Ge, who is currently a Professor
at The University of Florida. I worked for Dr. Ge from the fall
of my sophomore year until the summer before my Junior year.
During my time with Dr. Ge, I was involved with the ET project
(Exo-planet Tracker). The main goal of this project was to survey
the sky for extra-solar planets using radial velocity techniques.
I was cited in one manuscript for the
SPIE
conference in Glasgow
2004, this can be found in the publications section; much thanks
to Julian van Eyken for putting me on this manuscript.
I also worked with Junfeng Wang, a graduate student at Penn State,
on detections of the 2175 A dust feature. We used data from the
Sloan Digital Sky Survey, we looked for this broad absorption
feature in the Mg II absorption systems rest-frame. For more on
this, please visit the publications section for the abstract.
Searching for Pulsars...
I worked for
Dr. Alex Wolszczan
, Evan Pugh Professor of Astronomy
& Astrophysics at Penn State. I was involved in pulsar searches
with the Arecibo radio telescope in Puerto Rico. We used the PSPM
(Penn State Pulsar Machine) which is installed on the Arecibo
telescope to reduce and analyze the data. The PSPM, a 2 x 128 x
60 kHz filter-bank spectrometer can be used to record data in 2
different modes. In "search mode," data are continuously sampled
every 80 x 10-6 s with four-bit precision for each of the 128
frequency channels. Off-line processing proceeds first by
producing a de-dispersed time series in which successive channels
are delayed in time by an amount corresponding to the nominal
dispersion measure (DM) of each pulsar. The time series can then
either be searched for periodic signals or folded given a particular
pulse period to produce an integrated pulse profile.
In "timing mode," a custom-built chip is used to fold the incoming
data for each frequency channel on-line. The resulting 128
profiles are then de-dispersed and summed to produce a single
profile. In both operating modes, the PSPM is synchronized to
start on a well-calibrated 10s tick pulse so that all data can be
used for timing purposes. For a more information on pulsars, go
the this link.
Numerical Relativity...
I also worked in the Penn State
Numerical Relativity Group
with Dr. Pablo Laguna
and Dr. Deirdre Shoemaker.
We concentrate on Numerical Relativity (NR), where you solve
Einstein's equations with computers. Here is a little more detail
on what I did at the Institute.
In general relativity spacetime is considered to be
a curved four-dimensional Lorentzian manifold. The geometry i.e.
curvature, of spacetime is related to the distribution of matter
and energy by the Einstein equation,
Gab
= 8pTab.,
, with the Einstein tensor,
Gab
= Rab
- 1/2 gab
R,
being the trace reduced Ricci tensor
for the four-dimensional manifold and the stress-energy tensor
Tab
.
This equation treats time and space variables on an equal base.
A convenient way to solve Einstein equations numerically is to
write them in the form of a Cauchy problem. Then we have to find
an appropriate initial data set of basic variables according to
some initial value equations specifying constraints on the initial
data. We can evolve this data set by evolution equations, i.e.
equations specifying time derivatives for the basic variables.
We implement Einstein Equations in Arnowitt, Deser, and Misner
(ADM) 3+1 Formulation. In this formulation, you develop the
four-dimensional spacetime (M,g) into a family of spacelike
three-dimensional hypersurfaces. These can be parameterized by a
time parameter t. For infinitesimally separated events, the metric
of spacetime is:
ds2 = gam(dxa
+ badt)(dxm
+ bmdt)
- a2dt2,
What I did in terms of the 3+1 formulation was to adjust the
initial data by placing a gaussian in the spacetime metric close to a
puncture black hole. I then adjusted the amplitude of the gaussian in
powers of 10 and noted at what point in time the code broke down. This project
is being continued at the Institute since I left half-way through.
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