Department of Physicshttp://hdl.handle.net/1957/138312015-03-06T09:18:27Z2015-03-06T09:18:27ZPhotospheric emission from long duration gamma-ray bursts powered by variable enginesLópez-Cámara, DiegoMorsony, Brian J.Lazzati, Davidehttp://hdl.handle.net/1957/552382015-03-02T19:55:59Z2014-08-11T00:00:00ZPhotospheric emission from long duration gamma-ray bursts powered by variable engines
López-Cámara, Diego; Morsony, Brian J.; Lazzati, Davide
We present the results of a set of numerical simulations of long-duration gamma-ray burst
jets aimed at studying the effect of a variable engine on the peak frequency of the photospheric
emission. Our simulations follow the propagation of the jet inside the progenitor star,
its break-out, and the subsequent expansion in the environment out to the photospheric radius.
A constant and two step-function models are considered for the engine luminosity. We show
that our synthetic light-curves follow a luminosity-peak frequency correlation analogous to
the Golenetskii correlation found in long-duration gamma-ray burst observations. Within the
parameter space explored, it appears that the central engine luminosity profile does not have
a significant effect on the location of a gamma-ray burst in the Luminosity-peak frequency
plane, bursts from different central engines being indistinguishable from each other.
This is an author's peer-reviewed final manuscript, as accepted by the publisher. This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Oxford University Press on behalf of the Royal Astronomical Society. The published article can be found at: http://mnras.oxfordjournals.org/.
2014-08-11T00:00:00ZTerahertz induced transparency in single-layer graphenePaul, Michael J.Lee, ByounghwakWardini, Jenna L.Thompson, Zachary J.Stickel, Andrew D.Mousavian, AliChoi, HyunyongMinot, Ethan D.Lee, Yun-Shikhttp://hdl.handle.net/1957/549192015-01-15T23:50:42Z2014-12-01T00:00:00ZTerahertz induced transparency in single-layer graphene
Paul, Michael J.; Lee, Byounghwak; Wardini, Jenna L.; Thompson, Zachary J.; Stickel, Andrew D.; Mousavian, Ali; Choi, Hyunyong; Minot, Ethan D.; Lee, Yun-Shik
We show that the transmission of a terahertz (THz) pulse through single-layer graphene is strongly
nonlinear. As the peak electric field of the THz pulse exceeds 50 kV/cm, the graphene becomes
increasingly transparent to the THz radiation. When field strength reaches 800 kV/cm, the increased
transparency corresponds to a two-fold decrease in the time-average sheet conductivity of the graphene
(time averaged over the duration of the pulse). Time-resolved measurements reveal that the
leading portion of the pulse creates transparency for the trailing portion, with a 10-fold suppression
in sheet conductivity at the tail of the strongest THz pulse. Comparing the THz-induced transparency
phenomena in different sample geometries shows that substrate-free graphene is the best geometry
for maximizing the nonlinear transparency effect.
This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics Publishing and can be found at: http://scitation.aip.org/content/aip/journal/apl;jsessionid=5e5u4415ethj6.x-aip-live-03.
2014-12-01T00:00:00ZApproach to approximating the pair distribution function of inhomogeneous hard-sphere fluidsLurie-Gregg, PahoSchulte, Jeff B.Roundy, Davidhttp://hdl.handle.net/1957/545982014-12-08T19:33:01Z2014-10-21T00:00:00ZApproach to approximating the pair distribution function of inhomogeneous hard-sphere fluids
Lurie-Gregg, Paho; Schulte, Jeff B.; Roundy, David
We introduce an approximation for the pair distribution function of the inhomogeneous hard sphere fluid. Our
approximation makes use of our recently published averaged pair distribution function at contact, which has
been shown to accurately reproduce the averaged pair distribution function at contact for inhomogeneous density
distributions. This approach achieves greater computational efficiency than previous approaches by enabling the
use of exclusively fixed-kernel convolutions and thus allowing an implementation using fast Fourier transforms.
We compare results for our pair distribution approximation with two previously published works and Monte
Carlo simulation, showing favorable results.
This is the publisher’s final pdf. The published article is copyrighted by the American Physical Society and can be found at: http://journals.aps.org/pre/.
2014-10-21T00:00:00ZThe contact value approximation to the pair distribution function for an inhomogeneous hard sphere fluidLurie-Gregg, Pahohttp://hdl.handle.net/1957/545492014-12-05T15:07:23Z2014-10-03T00:00:00ZThe contact value approximation to the pair distribution function for an inhomogeneous hard sphere fluid
Lurie-Gregg, Paho
We construct the contact value approximation (CVA) for the pair distribution function,
g(²)(r₁, r₂), for an inhomogeneous hard sphere fluid. The CVA is an average of two radial
distribution functions, which each take as input the distance between the particles, |r₂ −r₁|,
and the average value of the radial distribution function at contact, gσ(r) at the locations
of each of the particles. In a recently published paper, an accurate function for gσ(r) was
developed, and it is made use of here. We then make a separable approximation to the
radial distribution function, gS(r), which we use to construct the separable contact value
approximation (CVA-S) to the pair distribution function.
We compare the CVA and CVA-S to Monte Carlo simulations that we have developed and
run as well as to two prior approximations to the pair distribution function. This comparison
is done in three main cases: When one particle is near a hard wall; when there is an external
particle the size of a sphere of the fluid; and for various integrals that illustrate typical use-cases
of the pair distribution function. We show reasonable quantitative agreement between
the CVA-S and simulation data, similar to that of the prior approximations. However, due
to its separable nature, the CVA-S can be efficiently used in density functional theory, which
is not the case of the prior approximations.
2014
2014-10-03T00:00:00Z