See website for show times and performances for the public.
Dr. Wang and Dr. Cleaver will be leading a weekly series of discussions on the book "String Theory and M-Theory: A Modern Introduction" by Katrin Becker, Melanie Becker, and John H. Schwartz (Amazon link).
See website for dates and times of public performances.
See website for dates and times of public performances.
See website for dates and times of public performances.
A Discussion on Black Holes and Stars in Horava-Lifshitz Theory with Projectability Condition
There have been many attempts to formulate a quantum theory of gravity. In this talk, I will introduce the subject of Horava-Lifshitz gravity and review some of its main characteristics as one of these theoretical formulations. Using a recent paper, Black holes and stars in Horava-Lifshitz theory with projectability condition, we will discuss application of this theory to one of the most studied topics in relativistic physics: Black Hole solutions.
The Influence of the Monomer Shape in the First Stage of Dust Growth in the Protoplanetary Disk
Laboratory experiments have shown that the initial stage of the dust growth in the protoplanetary disk starts with low-velocity hit-and-stick collisions between sub-micron grains, before the relative impact energy becomes large enough to cause the morphological restructuring of the forming aggregates. The results of these collisions are loose aggregates characterized by fractal dimensions ≤2. Numerical studies generally model this early stage with colliding clusters made of monodisperse spherical monomers. A paper is reviewed that aims to investigate how a more complex representation of the monodisperse monomers structure influences the morphology of the final aggregate particles in terms of fractal dimension, porosity, cross-section, and friction time. The study had also the purpose of testing the validity of the current fractal models in representing irregular particles.
We present here some new results about a systematic approach to higher-order gravity (HOG)
models. The HOG models are derived from curvature invariants that are more general than the
Einstein-Hilbert action. Some of the models exhibit late-time cosmic acceleration without the need for
dark energy and fit some current observations. The open question is that there are an infinite number of
invariants that one could select, and many of the published papers have stressed the need to find a
systematic approach that will allow one to study methodically the various possibilities. We explore a
new connection that we made between theorems from the theory of invariants in general relativity and
these cosmological models. In summary, the theorems demonstrate that curvature invariants are not all
independent from each other and that for a given Ricci Segre type and Petrov type (symmetry
classification) of the space-time, there exists a complete minimal set of independent invariants (a basis)
in terms of which all the other invariants can be expressed. As an immediate consequence of the
proposed approach, the number of invariants to consider is dramatically reduced from infinity to four
invariants in the worst case and to only two invariants in the cases of interest, including all Friedmann-
Lemaitre-Robertson-Walker metrics. We derive models that pass stability and physical acceptability
conditions. We derive dynamical equations and phase portrait analyses that show the promise of the
systematic approach. We consider observational constraints from magnitude-redshift Supernovae Type
Ia data, distance to the last scattering surface of the Cosmic Microwave Background radiation, and
Baryon Acoustic Oscillations. We seek to find models that pass physical and observational constraints
and give fits to the data that are almost as good as those of the standard Lambda-Cold-Dark-Matter model.
Jacob Moldenhauer is a graduate student in physics at the University of Texas at Dallas. He is a
member of Dr. Mustapha Ishak's Relativity, Cosmology and Astrophysics group. Jacob is expecting to
receive his Ph.D. in summer of 2010. His areas of research interest include the study of the cosmic
acceleration, whether due to a cosmological constant, dark energy, or modification of gravity on large
scales of distances. He is also interested in comparing cosmological models such as these to related
observational probes for expansion history and growth of structure, such as supernovae, baryon
acoustic oscillations, cosmic microwave background radiation, matter power spectrum, weak lensing,
as well as local, solar system tests of gravity.
Saturn's giant moon Titan has been of considerable interest
since the presence of an atmosphere was hinted at one century
ago. The NASA-ESA-ASI Cassini-Huygens mission, at Saturn for
the last 6 years, has transformed this curious dot in the sky
into a remarkably diverse, complex and interesting world, which
is in many ways more Earth-like than anywhere in the solar system.
This talk will summarize some of Cassini's recent findings
with emphasis on the interactions between Titan's surface
and atmosphere. These include dune-covered sand seas, river
channels that attest to violent but perhaps rare downpours
and climate change, and unevenly-distributed lakes of liquid
hydrocarbon that may attest to climate change on seasonal
and astronomical timescales.
Ralph Lorenz has a B.Eng. in Aerospace Systems Engineering
from the University of Southampton in the UK and a Ph.D. in
Physics in 1994 from the University of Kent at Canterbury. He worked
1990-1991 for the European Space Agency on the design of the Huygens
probe and during his PhD research designed and built its
penetrometer instrument that 12 years later measured the
mechanical properties of Titan's surface when Huygens landed in
January 2005. From 1994-2006 he worked as a planetary scientist at
the Lunar and Planetary Laboratory, University of Arizona with
particular interests in Titan, Mars, planetary climate, nonequilibrium
thermodynamics, aerospace vehicles and radar. He continues to work
on those topics at the Johns Hopkins University Applied Physics Laboratory
in Laurel, MD. He is on the editorial board of the International
Journal of Astrobiology and is author or co-author of several books
including 'Lifting Titan's Veil','Spinning Flight', and 'Space
Systems Failures' as well as over 140 publications in refereed journals.
Among the strongest sources of possible gravitational wave signals are
the mergers of binary systems containing compact objects such as
neutron stars or black holes. Further, one of the likeliest
candidates for the central engines of short, hard, gamma ray bursts is
the merger of binary neutron star systems. Thus, understanding such
mergers is possibly crucial for understanding some of the most
energetic events in the universe. However, understanding such systems
will require coming to grips with the intersection and interaction of
a wide swath of physics including magnetohydrodynamics, radiative
transfer, nuclear physics and general relativity. While such a
comprehensive approach is still a considerable way off, we will
attempt to describe some of our preliminary efforts in modeling binary
systems of compact objects together with some of this crucial physics.
To support the Mathematica site license at Baylor University,
Wolfram Research will be on campus Tuesday, April 20 to provide
training for Mathematica 7. This training session will be held
from 3pm to 4pm in the Sid Richardson Builidng, SR 344. There
will be time after the training session to answer technical and
licensing questions about Mathematica.
Mathematica is often thought of as useful for only math, but this
training session will illustrate why Version 7 changes the
pedagogy of teaching within biology, chemistry, economics,
physics, engineering, and a number of other academic departments.
The training session will focus on ideas for creating universal
examples in Mathematica that can be used by colleagues or
students with no prior Mathematica experience.
The content will help attendees with no prior experience get
started with the Mathematica language and workflow. Since there
is a large amount of new functionality in Version 7, most
intermediate and advanced users who attend these training
sessions have reported learning quite a bit as well. All
attendees will receive an electronic copy of the examples, which
can be adapted to individual projects.
Students are also welcome at this training session; please invite
any students in your courses.
The foundations for modern astronomy, including the Equatorial and Ecliptic coordinate systems, the constellations and Zodiac, are laid by the Sumerians and Babylonians. In 499 BC a luni-solar calendar appears, based on the discovery that 235 synodic months = 19 solar years, accurate to 2 hours over the 19 year period!
The Greek astronomer Hipparchus introduces spherical trigonometry, discovers the precession of the Earth's axis, and develops the stereographic projection. Aristarchus proposes a heliocentric model of the universe, estimates the size of the Moon, and the distance from the Earth to the Sun.
A classical dusty plasma experiment was performed using two
> different dust grain sizes to form a strongly coupled asymmetric
> bilayer (two closely spaced interacting monolayers) of two species
> of charged dust particles. The observation and analysis of the
> thermally excited particle oscillations revealed the collective
> mode structure and dispersion (wave propagation) in this system; in
> particular, the existence of the theoretically predicted k = 0
> energy (frequency) gap was verified. Equilibrium molecular-dynamics
> simulations were performed to emulate the experiment, assuming
> Yukawa-type interparticle interaction. The simulations and analytic
> calculations based both on lattice summation and on the
> quasilocalized charge approximation approach are in good agreement
> with the experimental findings and help in identifying and
> characterizing the observed phenomena.
Peter Hartmann received the Ph.D. degree in physics from Etvs Lornd University, Budapest, Hungary, in 2004. He is a Research Fellow with the Research Institute for Solid State Physics and Optics of the Hungarian Academy of Sciences. His research interests include experimental and simulational investigations of elementary processes in low-pressure gas discharges and strongly coupled plasmas with special emphasis on the physics of laboratory dusty plasmas.
Part II (3:30 pm, Friday April 23, 344SR)
Nicolaus Copernicus, a Church canon, puts forth the hypothesis that the Earth goes around the Sun, and dedicates the work to Pope Paul III. "The Copernican Hypothesis" quickly gets embroiled in the turmoil of the Reformation.
Tycho Brahe, a Danish nobleman, carries out extensive and accurate "Naked Eye" observations of the Sun and planets. He builds giant machines, compensates for refraction by the Earth's atmosphere, and aspires to a level of accuracy of 1 arcminute. After the death of Fredrick II of Denmark, he goes to Prague with the support of Rudolph II, the Holy Roman Emperor.
Johannes Kepler begins studies in Theology at Tbingen, but soon switches to astronomy and mathematics, defending the Copernican hypothesis in student debates. He obtains a teaching position at a seminary in Graz, but later leaves, rather than convert to Catholicism, and takes a position with Brahe. Examining Brahe's data for Mars, he concludes that its orbit is elliptical. His three fundamental laws of planetary motion, deduced from Brahe's data over many years, guide Newton to the inverse square law of gravity.
Abstract: Finite element approximations for the eigenvalue problem of
the Laplace operator is discussed. A gradient recovery scheme is proposed
to enhance the nite element solutions of the eigenvalues. By reconstruct-
ing the numerical solution and its gradient, it is possible to produce more
accurate numerical eigenvalues. Furthermore, the recovered gradient can
be used to form an a posteriori error estimator to guide an adaptive mesh
refinement. Therefore, this method works not only for structured meshes,
but also for unstructured and adaptive meshes.
Additional computational cost for this post-processing technique is only
O(N) (N is the total degrees of freedom), comparing with O(N2) cost for
the original problem.
Theoretical results can be summarized in the following:
1) For sufficiently smooth eigenfunctions. Under uniform meshes or the
Delaunay triangulation with regular refinement, the enhanced eigenvalue
approximations for the linear element converge at rate O(h4) (h is the max-
imum mesh size), while the original approximations converge at rate O(h2).
2) For eigenfunctions with corner singularities. Under a commonly used
adaptive mesh renement strategy, the enhanced eigenvalue approximations
converge at rate O(Nk=21/2) for some 1/2 > 0 (k = 1 for the linear ele-
ment and k = 2 for the quadratic element), while the adaptive eigenvalue
approximations converge at rate O(Nk=2).
All above theoretical results are numerically verified. Furthermore, the
method can be applied to general second-order elliptic operators, fourth-
order and higher-order partial differential operators.
Jacob Jantzi: "Translational and Rotational Velocity Statistics in a Rotating Granular Tumbler"
Stephen Pickett: "Thermophoresis Experiments in Complex Plasma Containing Multiple Dust Cycles"