270 research outputs found
Regulation as a Redistributive Policy: A Political Economy Approach
In this thesis, I study the use of regulation as a redistributive policy and its implications on economic and political outcomes.
In the first chapter of this thesis, I remark that regulation has distributive and welfare consequences, making it a powerful political tool. I show that when the regulation is on goods for which all of the citizens have similar consumption behaviour, a highly unequal society funds the costs of those goods mostly through general taxation; instead of tariffs charged to users. Importantly, when the poor have access to only the essential goods in the economy, regulation becomes a strong political tool, and it is poverty rather than inequality that determines the use of regulation.
In the second chapter, I start with the observation that corporations devote costly efforts to gain access to candidates before elections. These pre-electoral attempts take many forms and commonly result in a welfare loss. Then, I explore the consequences of the access of a monopolistic firm to a candidate on the regulatory policy. I show that when the firm transfers a private interest to a popular candidate, regulation results in gains for both the firm and the candidate; and a welfare loss for the voters. Instead, this welfare loss does not take place when the firm uses campaign contributions as signals to communicate private information. From this perspective, there are benefits in permitting interest groups to fund political campaigns.
The third chapter is motivated by the fact that developing countries subsidise the tariffs of public utilities such as electricity or transportation with high costs in terms of the quality and sustainability of the utility provisions. Even when governments repeatedly claim that the main goal of these subsidies is to improve the well-being of the poor, most literature has explained the use of these tools is driven by income inequality rather than the poverty rate. In contrast, I study the effect of the size of the poor on the choice of the mix of regulation and other traditional forms of redistributive policy. I begin by showing that the poor are better characterised by their consumption bundle than their income. Consequently, when the public utilities are essential for the poor, a higher poverty rate leads to a larger amount of subsidies to utilities and a smaller size of income redistribution
Turbulent Linewidths as a Diagnostic of Self-Gravity in Protostellar Discs
We use smoothed particle hydrodynamics simulations of massive protostellar
discs to investigate the predicted broadening of molecular lines from discs in
which self-gravity is the dominant source of angular momentum transport. The
simulations include radiative transfer, and span a range of disc-to-star mass
ratios between 0.25 and 1.5. Subtracting off the mean azimuthal flow velocity,
we compute the distribution of the in-plane and perpendicular peculiar velocity
due to large scale structure and turbulence induced by self-gravity. For the
lower mass discs, we show that the characteristic peculiar velocities scale
with the square root of the effective turbulent viscosity parameter, as
expected from local turbulent-disc theory. The derived velocities are
anisotropic, with substantially larger in-plane than perpendicular values. As
the disc mass is increased, the validity of the locally determined turbulence
approximation breaks down, and this is accompanied by anomalously large
in-plane broadening. There is also a high variance due to the importance of
low-m spiral modes. For low-mass discs, the magnitude of in-plane broadening
is, to leading order, equal to the predictions from local disc theory and
cannot constrain the source of turbulence. However, combining our results with
prior evaluations of turbulent broadening expected in discs where the
magnetorotational instability (MRI) is active, we argue that self-gravity may
be distinguishable from the MRI in these systems if it is possible to measure
the anisotropy of the peculiar velocity field with disc inclination.
Furthermore, for large mass discs, the dominant contribution of large-scale
modes is a distinguishing characteristic of self-gravitating turbulence versus
MRI driven turbulence.Comment: 8 pages, 13 figures, accepted for publication in MNRA
Warp propagation in astrophysical discs
Astrophysical discs are often warped, that is, their orbital planes change
with radius. This occurs whenever there is a non-axisymmetric force acting on
the disc, for example the Lense-Thirring precession induced by a misaligned
spinning black hole, or the gravitational pull of a misaligned companion. Such
misalignments appear to be generic in astrophysics. The wide range of systems
that can harbour warped discs - protostars, X-ray binaries, tidal disruption
events, quasars and others - allows for a rich variety in the disc's response.
Here we review the basic physics of warped discs and its implications.Comment: To be published in Astrophysical Black Holes by Haardt et al.,
Lecture Notes in Physics, Springer 2015. 19 pages, 2 figure
The vertical structure of T Tauri accretion discs IV. Self-irradiation of the disc in the FU Orionis outburst phase
I investigate the self-irradiation of intensively accreting circumstellar
discs (backwarmed discs). It is modelled using the two-layer disc approach by
Lachaume et al. (2003) that includes heating by viscous dissipation and by an
external source of radiation. The disc is made of a surface layer directly
heated by the viscous luminosity of the central parts of the disc, and of an
interior heated by viscosity as well as by reprocessed radiation from the
surface. This model convincingly accounts for the infrared excess of some FU
Orionis objects in the range 1-200 microns and supports the backwarmed disc
hypothesis sometimes invoked to explain the mid- and far-infrared excesses
whose origins are still under debate. Detailed simulation of the vertical
radiative transfert in the presence of backwarming is still needed to
corroborate these results and spectroscopically constrain the properties of
intensively accreting discs.Comment: 6 pages, 2 figures, 2 tables, accepted by Astronomy & Astrophysic
Millimeter imaging of HD 163296: probing the disk structure and kinematics
We present new multi-wavelength millimeter interferometric observations of
the Herbig Ae star HD 163296 obtained with the IRAM/PBI, SMA and VLA arrays
both in continuum and in the 12CO, 13CO and C18O emission lines. Gas and dust
properties have been obtained comparing the observations with self-consistent
disk models for the dust and CO emission. The circumstellar disk is resolved
both in the continuum and in CO. We find strong evidence that the circumstellar
material is in Keplerian rotation around a central star of 2.6 Msun. The disk
inclination with respect to the line of sight is 46+-4 deg with a position
angle of 128+-4 deg. The slope of the dust opacity measured between 0.87 and 7
mm (beta=1) confirms the presence of mm/cm-size grains in the disk midplane.
The dust continuum emission is asymmetric and confined inside a radius of 200
AU while the CO emission extends up to 540 AU. The comparison between dust and
CO temperature indicates that CO is present only in the disk interior. Finally,
we obtain an increasing depletion of CO isotopomers from 12CO to 13CO and C18O.
We argue that these results support the idea that the disk of HD 163296 is
strongly evolved. In particular, we suggest that there is a strong depletion of
dust relative to gas outside 200 AU; this may be due to the inward migration of
large bodies that form in the outer disk or to clearing of a large gap in the
dust distribution by a low mass companion.Comment: Accepted for publication on A&A, 16 page
Chaotic star formation and the alignment of stellar rotation with disc and planetary orbital axes
We investigate the evolution of the relative angle between the stellar
rotation axis and the circumstellar disc axis of a star that forms in a stellar
cluster from the collapse of a turbulent molecular cloud. This is an inherently
chaotic environment with variable accretion, both in terms of rate and the
angular momentum of the material, and dynamical interactions between stars. We
find that the final stellar rotation axis and disc spin axis can be strongly
misaligned, but this occurs primarily when the disc is truncated by a dynamical
encounter so that the final disc rotation axis depends simply on what fell in
last. This may lead to planetary systems with orbits that are misaligned with
the stellar rotation axis, but only if the final disc contains enough mass to
form planets. We also investigate the time variability of the inner disc spin
axis, which is likely to determine the direction of a protostellar jet. We find
that the jet direction varies more strongly for lighter discs, such as those
that have been truncated by dynamical interactions or have suffered a period of
rapid accretion. Finally, we note that variability of the angular momentum of
the material accreting by a star implies that the internal velocity field of
such stars may be more complicated than that of aligned differential rotation.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
A Numerical Study of Brown Dwarf Formation via Encounters of Protostellar Disks
The formation of brown dwarfs (BDs) due to the fragmentation of proto-stellar
disks undergoing pairwise encounters was investigated. High resolution allowed
the use of realistic initial disk models where both the vertical structure and
the local Jeans mass were resolved. The results show that objects with masses
ranging from giant planets to low mass stars can form during such encounters
from initially stable disks. The parameter space of initial spin-orbit
orientations and the azimuthal angles for each disk was explored. An upper
limit on the initial Toomre Q value of ~2 was found for fragmentation to occur.
Depending on the initial configuration, shocks, tidal-tail structures and mass
inflows were responsible for the condensation of disk gas. Retrograde disks
were generally more likely to fragment. When the interaction timescale was
significantly shorter than the disks' dynamical timescales, the proto-stellar
disks tended to be truncated without forming objects.
The newly-formed objects had masses ranging from 0.9 to 127 Jupiter masses,
with the majority in the BD regime. They often resided in star-BD multiples and
in some cases also formed hierarchical orbiting systems. Most of them had large
angular momenta and highly flattened, disk-like shapes. The objects had radii
ranging from 0.1 to 10 AU. The disk gas was assumed to be locally isothermal,
appropriate for the short cooling times in extended proto-stellar disks, but
not for condensed objects. An additional case with explicit cooling that
reduced to zero for optically thick gas was simulated to test the extremes of
cooling effectiveness and it was still possible to form objects in this case.
Detailed radiative transfer is expected to lengthen the internal evolution
timescale for these objects, but not to alter our basic results.Comment: 18 pages, 12 figures and 2 tables. Accepted for publication in MNRA
The Effects of Accretion Luminosity upon Fragmentation in the Early Universe
We introduce a prescription for the luminosity from accreting protostars into
smoothed particle hydrodynamics simulation, and apply the method to simulations
of five primordial minihalos generated from cosmological initial conditions. We
find that accretion luminosity delays fragmentation within the halos, but does
not prevent it. In halos that slowly form a low number of protostars, the
accretion luminosity can reduce the number of fragments that are formed before
the protostars start ionising their surroundings. However, halos that rapidly
form many protostars become dominated by dynamical processes, and the effect of
accretion luminosity becomes negligible. Generally the fragmentation found in
the halos is highly dependent on the initial conditions. Accretion luminosity
does not substantially affect the accretion rates experienced by the
protostars, and is far less important than dynamical interactions, which can
lead to ejections that effectively terminate the accretion. We find that the
accretion rates onto the inner regions of the disks (20 AU) around the
protostars are highly variable, in contrast to the constant or smoothly
decreasing accretion rates currently used in models of the pre-main sequence
evolution of Population III stars.Comment: 12 pages, 10 figures and 3 tables. Accepted by MNRA
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