3,726 research outputs found
Policy Considerations for the New Zealand Natural Gas Industry
Professor Stanford Levin and Alfred Duncan undertake a study of the natural gas industry in New Zealand at a time when the two industry regulators are undertaking regulatory initiatives.The Commerce Commission is in the midst of setting their default price-quality regulatory framework that will take effect in July 2012. The Gas Industry Company the industry co-regulator has just recently issued a proposal to undertake a project to determine the current need for gas transmission investment and to develop a way for any needed investment to occur.The authors are hopeful that this study will prove useful to industry participants policymakers and also to the two industry regulators
On the Quasi-Periodic Oscillations of Magnetars
We study torsional Alfv\'en oscillations of magnetars, i.e., neutron stars
with a strong magnetic field. We consider the poloidal and toroidal components
of the magnetic field and a wide range of equilibrium stellar models. We use a
new coordinate system (X,Y), where ,
and is the radial component of the magnetic
field. In this coordinate system, the 1+2-dimensional evolution equation
describing the quasi-periodic oscillations, QPOs, see Sotani et al. (2007), is
reduced to a 1+1-dimensional equation, where the perturbations propagate only
along the Y-axis. We solve the 1+1-dimensional equation for different boundary
conditions and open magnetic field lines, i.e., magnetic field lines that reach
the surface and there match up with the exterior dipole magnetic field, as well
as closed magnetic lines, i.e., magnetic lines that never reach the stellar
surface. For the open field lines, we find two families of QPOs frequencies; a
family of "lower" QPOs frequencies which is located near the X-axis and a
family of "upper" frequencies located near the Y-axis. According to Levin
(2007), the fundamental frequencies of these two families can be interpreted as
the turning points of a continuous spectrum. We find that the upper frequencies
are constant multiples of the lower frequencies with a constant equaling 2n+1.
For the closed lines, the corresponding factor is n+1 . By these relations, we
can explain both the lower and the higher observed frequencies in SGR 1806-20
and SGR 1900+14.Comment: 8 pages, 7 figure
Alfv\'en Polar Oscillations of Relativistic Stars
We study polar Alfv\'en oscillations of relativistic stars endowed with a
strong global poloidal dipole magnetic field. Here we focus only on the
axisymmetric oscillations which are studied by evolving numerically the
two-dimensional perturbation equations. Our study shows that the spectrum of
the polar Alfv\'{e}n oscillations is discrete in contrast to the spectrum of
axial Alfv\'{e}n oscillations which is continuous. We also show that the
typical fluid modes, such as the f and p modes, are not significantly affected
by the presence of the strong magnetic field.Comment: 10 pages, 5 figure
Magnetar Oscillations I: strongly coupled dynamics of the crust and the core
Quasi-Periodic Oscillations (QPOs) observed during Soft Gamma Repeaters giant
flares are commonly interpreted as the torsional oscillations of magnetars. The
oscillatory motion is influenced by the strong interaction between the shear
modes of the crust and Alfven-like modes in the core. We study the dynamics
which arises through this interaction, and present several new results: (1) We
show that global {\it edge modes} frequently reside near the edges of the core
Alfven continuum. (2) We compute the magnetar's oscillatory motion for
realistic axisymmetric magnetic field configurations and core density profiles,
but with a simplified model of the elastic crust. We show that one may
generically get multiple gaps in the Alfven continuum. One obtains discrete
global {\it gap modes} if the crustal frequencies belong to the gaps. (3) We
show that field tangling in the core enhances the role of the core discrete
Alfven modes and reduces the role of the core Alfven continuum in the overall
oscillatory dynamics of the magnetar. (4) We demonstrate that the system
displays transient and/or drifting QPOs when parts of the spectrum of the core
Alfven modes contain discrete modes which are densely and regularly spaced in
frequency. (5) We show that if the neutrons are coupled into the core Alfven
motion, then the post-flare crustal motion is strongly damped and has a very
weak amplitude. Thus magnetar QPOs give evidence that the proton and neutron
components in the core are dynamically decoupled and that at least one of them
is a quantum fluid. (6) We show that it is difficult to identify the
high-frequency 625 Hz QPO as being due to the physical oscillatory mode of the
magnetar, if the latter's fluid core consists of the standard
proton-neutron-electron mixture and is magnetised to the same extent as the
crust. (Abstract abridged)Comment: 22 pages, 22 figures, submitted to MNRA
Magnetar Oscillations II: spectral method
The seismological dynamics of magnetars is largely determined by a strong
hydro-magnetic coupling between the solid crust and the fluid core. In this
paper we set up a "spectral" computational framework in which the magnetar's
motion is decomposed into a series of basis functions which are associated with
the crust and core vibrational eigenmodes. A general-relativistic formalism is
presented for evaluation of the core Alfven modes in the magnetic-flux
coordinates, as well for eigenmode computation of a strongly magnetized crust
of finite thickness. By considering coupling of the crustal modes to the
continuum of Alfven modes in the core, we construct a fully relativistic
dynamical model of the magnetar which allows: i) Fast and long simulations
without numerical dissipation. ii) Very fine sampling of the stellar structure.
We find that the presence of strong magnetic field in the crust results in
localizing of some high-frequency crustal elasto-magnetic modes with the radial
number n>1 to the regions of the crust where the field is nearly horizontal.
While the hydro-magnetic coupling of these localized modes to the Alfven
continuum in the core is reduced, their energy is drained on a time-scale much
less than 1 second. Therefore the puzzle of the observed QPOs with frequencies
larger than 600 Hz still stands.Comment: 15 pages, 11 figures, submitted to MNRA
Shear modulus of neutron star crust
Shear modulus of solid neutron star crust is calculated by thermodynamic
perturbation theory taking into account ion motion. At given density the crust
is modelled as a body-centered cubic Coulomb crystal of fully ionized atomic
nuclei of one type with the uniform charge-compensating electron background.
Classic and quantum regimes of ion motion are considered. The calculations in
the classic temperature range agree well with previous Monte Carlo simulations.
At these temperatures the shear modulus is given by the sum of a positive
contribution due to the static lattice and a negative contribution
due to the ion motion. The quantum calculations are performed for the first
time. The main result is that at low temperatures the contribution to the shear
modulus due to the ion motion saturates at a constant value, associated with
zero-point ion vibrations. Such behavior is qualitatively similar to the
zero-point ion motion contribution to the crystal energy. The quantum effects
may be important for lighter elements at higher densities, where the ion plasma
temperature is not entirely negligible compared to the typical Coulomb ion
interaction energy. The results of numerical calculations are approximated by
convenient fitting formulae. They should be used for precise neutron star
oscillation modelling, a rapidly developing branch of stellar seismology.Comment: 10 pages, 3 figures, accepted to MNRA
Policy Considerations for the New Zealand Natural Gas Industry
Professor Stanford Levin and Alfred Duncan undertake a study of the natural gas industry in New Zealand at a time when the two industry regulators are undertaking regulatory initiatives.The Commerce Commission is in the midst of setting their default price-quality regulatory framework that will take effect in July 2012. The Gas Industry Company the industry co-regulator has just recently issued a proposal to undertake a project to determine the current need for gas transmission investment and to develop a way for any needed investment to occur.The authors are hopeful that this study will prove useful to industry participants policymakers and also to the two industry regulators
Gravity-Driven Acceleration of the Cosmic Expansion
It is shown here that a dynamical Planck mass can drive the scale factor of
the universe to accelerate. The negative pressure which drives the cosmic
acceleration is identified with the unusual kinetic energy density of the
Planck field. No potential nor cosmological constant is required. This suggests
a purely gravity driven, kinetic inflation. Although the possibility is not
ruled out, the burst of acceleration is often too weak to address the initial
condition problems of cosmology. To illustrate the kinetic acceleration, three
different cosmologies are presented. One such example, that of a bouncing
universe, demonstrates the additional feature of being nonsingular. The
acceleration is also considered in the conformally related Einstein frame in
which the Planck mass is constant.Comment: 23 pages, LaTex, figures available upon request, (revisions include
added references and comment on inflation) CITA-94-1
Non-axisymmetric low frequency oscillations of rotating and magnetized neutron stars
We investigate non-axisymmetric low frequency modes of a rotating and
magnetized neutron star, assuming that the star is threaded by a dipole
magnetic field whose strength at the stellar surface, , is less than G, and whose magnetic axis is aligned with the rotation axis. For modal
analysis, we use a neutron star model composed of a fluid ocean, a solid crust,
and a fluid core, where we treat the core as being non-magnetic assuming that
the magnetic pressure is much smaller than the gas pressure in the core. Here,
we are interested in low frequency modes of a rotating and magnetized neutron
star whose oscillation frequencies are similar to those of toroidal crust modes
of low spherical harmonic degree and low radial order. For a magnetic field of
G, we find Alfv\'en waves in the ocean have similar frequencies
to the toroidal crust modes, and we find no -modes confined in the ocean for
this strength of the field. We calculate the toroidal crustal modes, the
interfacial modes peaking at the crust/core interface, and the core inertial
modes and -modes, and all these modes are found to be insensitive to the
magnetic field of strength B_0\ltsim10^{12}G. We find the displacement vector
of the core -modes have large amplitudes around the rotation
axis at the stellar surface even in the presence of a surface magnetic field
G, where and are the spherical harmonic degree
and the azimuthal wave number of the -modes, respectively. We suggest that
millisecond X-ray variations of accretion powered X-ray millisecond pulsars can
be used as a probe into the core -modes destabilized by gravitational wave
radiation.Comment: 15pages, 7 figure
CMS computing operations during run 1
During the first run, CMS collected and processed more than 10B data events and simulated more than 15B events. Up to 100k processor cores were used simultaneously and 100PB of storage was managed. Each month petabytes of data were moved and hundreds of users accessed data samples. In this document we discuss the operational experience from this first run. We present the workflows and data flows that were executed, and we discuss the tools and services developed, and the operations and shift models used to sustain the system. Many techniques were followed from the original computing planning, but some were reactions to difficulties and opportunities. We also address the lessons learned from an operational perspective, and how this is shaping our thoughts for 2015
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