53 research outputs found
Modeling the Large Scale Structures of Astrophysical Jets in the Magnetically Dominated Limit
We suggest a new approach that could be used for modeling both the large
scale behavior of astrophysical jets and the magnetically dominated explosions
in astrophysics. We describe a method for modeling the injection of magnetic
fields and their subsequent evolution in a regime where the free energy is
magnetically dominated. The injected magnetic fields, along with their
associated currents, have both poloidal and toroidal components, and they are
not force free. The dynamic expansion driven by the Lorentz force of the
injected fields is studied using 3-dimensional ideal magnetohydrodynamic
simulations. The generic behavior of magnetic field expansion, the interactions
with the background medium, and the dependence on various parameters are
investigated.Comment: Accepted to ApJ, May 10, 2006 issue, 12 figures total (3 color
figures
Campus Vol X N 2
Kull, Shaw. Cover. Picture. 1.
Howard Studio. Miss Gert Mahaffey . Picture. 2.
Anonymous. Kampus Calender . Picture. 5.
Hodges, John. Classroommanship: or The Art of Going to School Without Actually Learning Anything . Prose. 9.
Shine and K.B. Wimpus. It\u27s Tradition . Picture. 11.
Opie, Shaw. Harry and The Pirates . Cartoon. 12.
Knapp, Chuck. Ned the newsboy--A Christmas Fable . Prose. 14.
Anonymous. Our Miss Xmas Queen as Seen by... Picture. 15.
Rasor, Tip. How\u27d I do it? . Picture. 16.
Sherman, Marj. A Xmas Tale For Juvenile Delinquents . Prose. 18.
Anonymous. I Am the Very Model of a Modern College Sophomore . Poem. 19.
Anonymous. Do You Need Anything? . Picture. 20.
Fitch. The Down Hill General Backslide of Things While I was Away . Prose. 22.
Rasor, Tip. Solution . Prose. 22.
Kull, Shaw. untitled. Cartoon. 23.
Kitty Kat. Arizona . Cartoon. 24.
Banter, Colgate. Untitled. Cartoon. 24.
Gariffo and Marselle. Untitled. Cartoon. 24.
Kitty Kat. Untitled. Cartoon. 24.
Anonymous. Sport Short . Poem. 25.
Anonymous. Cully Hall Discovers Xmas fer Thinkin\u27 of Others . Prose. 26.
Decker, Mary and Marj Sherman. Untitled. Cartoon. 26
High Magnetic Shear Gain in a Liquid Sodium Stable Couette Flow Experiment; A Prelude to an alpha-Omega Dynamo
The -phase of the liquid sodium - dynamo experiment
at NMIMT in cooperation with LANL has successfully demonstrated the production
of a high toroidal field, from the radial
component of an applied poloidal magnetic field, . This enhanced toroidal
field is produced by rotational shear in stable Couette flow within liquid
sodium at . The small turbulence in stable Taylor-Couette flow
is caused by Ekman flow where . This high
-gain in low turbulence flow contrasts with a smaller -gain in
higher turbulence, Helmholtz-unstable shear flows. This result supports the
ansatz that large scale astrophysical magnetic fields are created within
semi-coherent large scale motions in which turbulence plays only a smaller
diffusive role that enables magnetic flux linkage.Comment: 5 pages, 5 figures, submitted PRL revised version: add one author,
minor typo'
Non-LTE time-dependent spectroscopic modelling of type II-plateau supernovae from the photospheric to the nebular phase: case study for 15 and 25Msun progenitor stars
We present the first non-LTE time-dependent radiative-transfer simulations of
supernovae (SNe) II-Plateau (II-P) covering both the photospheric and nebular
phases, from ~10 to >~1000d after the explosion, and based on 1.2B
piston-driven ejecta produced from a 15Msun and a 25Msun non-rotating
solar-metallicity star. The radial expansion of the gradually cooling
photosphere gives rise to a near-constant luminosity up to >~100d after
explosion. The photosphere remains in the outer 0.5Msun of the ejecta for up to
~50d after explosion. As the photosphere reaches the edge of the helium core,
the SN luminosity drops by an amount mitigated by the progenitor radius and the
56Ni mass. Synthetic light-curves exhibit a bell-shape morphology, evolving
faster for more compact progenitors, and with an earlier peak and narrower
width in bluer filters. UV and U-band fluxes are very sensitive to
line-blanketing, the metallicity, and the adopted model atoms. During the
recombination epoch synthetic spectra are dominated by HI and metal lines, and
are largely insensitive to the differing H/He/C/N/O composition of our two
progenitor stars. In contrast, synthetic nebular-phase spectra reveal a
broader/stronger OI doublet line in the higher-mass progenitor model,
reflecting the larger masses of oxygen and nickel that are ejected. Our
simulations overestimate the typical luminosity and the visual rise time of
standard SNe II-P, likely a consequence of our progenitor stars being too big
and/or too hydrogen rich. Comparison of our simulations with photospheric-phase
observations of SN1999em of the same color are satisfactory. Our neglect of
non-thermal processes leads to a fast disappearance of continuum radiation and
Balmer-line emission at the end of the plateau phase. With the exception of HI
lines, our nebular spectra show a striking similarity to contemporaneous
observations of SN1999em.Comment: Accepted to MNRA
Super-luminous supernovae: 56Ni power versus magnetar radiation
Much uncertainty surrounds the origin of super-luminous supernovae (SNe).
Motivated by the discovery of the Type Ic SN2007bi, we study its proposed
association with a pair-instability SN (PISN). We compute stellar-evolution
models for primordial ~200Msun stars, simulating the implosion/explosion due to
the pair-production instability, and use them as inputs for detailed non-LTE
time-dependent radiative-transfer simulations that include non-local energy
deposition and non-thermal processes. We retrieve the basic morphology of PISN
light curves from red-supergiant, blue-supergiant, and Wolf-Rayet (WR) star
progenitors. Although we confirm that a progenitor 100Msun helium core (PISN
model He100) fits well the SN2007bi light curve, the low ratios of its kinetic
energy and 56Ni mass to the ejecta mass, similar to standard core-collapse SNe,
conspire to produce cool photospheres, red spectra subject to strong line
blanketing, and narrow line profiles, all conflicting with SN2007bi
observations. He-core models of increasing 56Ni-to-ejecta mass ratio have bluer
spectra, but still too red to match SN2007bi, even for model He125 -- the
effect of 56Ni heating is offset by the associated increase in blanketing. In
contrast, the delayed injection of energy by a magnetar represents a more
attractive alternative to reproduce the blue, weakly-blanketed, and broad-lined
spectra of super-luminous SNe. The extra heat source is free of blanketing and
is not explicitly tied to the ejecta. Experimenting with a ~9Msun WR-star
progenitor, initially exploded to yield a ~1.6B SN Ib/c ejecta but later
influenced by tunable magnetar-like radiation, we produce a diversity of blue
spectral morphologies reminiscent of SN2007bi, the peculiar Type Ib SN2005bf,
and super-luminous SN2005ap-like events.Comment: 5 pages, 4 figures, paper accepted to MNRAS lette
Pulsar Recoil and Gravitational Radiation due to Asymmetrical Stellar Collapse and Explosion
New data imply that the average velocity of radio pulsars is large
\cite{hla93}. Under the assumption that these data imply that a pulsar is born
with an ``intrinsic'' kick, we investigate whether such kicks can be a
consequence of asymmetrical stellar collapse and explosion. We calculate the
gravitational wave (GW) signature of such asymmetries due to anisotropic
neutrino radiation and mass motions. We predict that any recoils imparted to
the neutron star at birth will result in a gravitational wave strain,
h, that does not go to zero with time. Hence, there may be
``memory'' \cite{bt87} in the gravitational waveform from a protoneutron star
that is correlated with its recoil and neutrino emissions.Comment: 13 Pages, APS REVTeX format, encapsulated postscript figures,
uuencoded and compressed. Accepted for publication in Phys. Rev. Letter
The medical student
The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine
Geology of the Wellsville quadrangle, New York,
no.326 (1942
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