45,407 research outputs found
A Tale of Two Distributions: From Few To Many Vortices In Quasi-Two-Dimensional Bose-Einstein Condensates
Motivated by the recent successes of particle models in capturing the
precession and interactions of vortex structures in quasi-two-dimensional
Bose-Einstein condensates, we revisit the relevant systems of ordinary
differential equations. We consider the number of vortices as a parameter
and explore the prototypical configurations ("ground states") that arise in the
case of few or many vortices. In the case of few vortices, we modify the
classical result of Havelock [Phil. Mag. , 617 (1931)] illustrating
that vortex polygons in the form of a ring are unstable for .
Additionally, we reconcile this modification with the recent identification of
symmetry breaking bifurcations for the cases of . We also briefly
discuss the case of a ring of vortices surrounding a central vortex (so-called
configuration). We finally examine the opposite limit of large and
illustrate how a coarse-graining, continuum approach enables the accurate
identification of the radial distribution of vortices in that limit.Comment: 15 pages, 2 figure
Gluino Air Showers as a Signal of Split Supersymmetry
It has been proposed recently that, within the framework of split
Supersymmetry, long lived gluinos generated in astrophysical sources could be
detected using the signatures of the air showers they produce, thus providing a
lower bound for their lifetime and for the scale of SUSY breaking. We present
the longitudinal profile and lateral spread of -hadron induced extensive air
showers and consider the possibility of measuring them with a detector with the
characteristics of the Pierre Auger Observatory.Comment: 4 pages, 3 eps figure
Indicators of Good Governance: Developing an Index of Governance Quality at the LGU Level
Governance is a complex concept. It includes the state’s institutions and structures, its decisionmaking process, its capacity to implement guidelines and the relationship between government officials and the public. Hence, this study attempts to develop a composite index of the quality of governance at the local government level. It also defines limited indicators, which can be measured consistently and can capture the substance of each dimension and their compatibility over time and space. The governance quality index constructed here is focused on three principal elements: capacity of the LGU to mobilize and utilize resources, efficiency and effectiveness of the LGU in the delivery of social services and presence of mechanism to ensure accountability.governance, local revenue, micro level accountability
Planetary Formation Scenarios Revistied: Core-Accretion Versus Disk Instability
The core-accretion and disk instability models have so far been used to
explain planetary formation. These models have different conditions, such as
planet mass, disk mass, and metallicity for formation of gas giants. The
core-accretion model has a metallicity condition ([Fe/H] > −1.17 in the
case of G-type stars), and the mass of planets formed is less than 6 times that
of the Jupiter mass MJ. On the other hand, the disk instability model does not
have the metallicity condition, but requires the disk to be 15 times more
massive compared to the minimum mass solar nebulae model. The mass of planets
formed is more than 2MJ. These results are compared to the 161 detected planets
for each spectral type of the central stars. The results show that 90% of the
detected planets are consistent with the core-accretion model regardless of the
spectral type. The remaining 10% are not in the region explained by the
core-accretion model, but are explained by the disk instability model. We
derived the metallicity dependence of the formation probability of gas giants
for the core-accretion model. Comparing the result with the observed fraction
having gas giants, they are found to be consistent. On the other hand, the
observation cannot be explained by the disk instability model, because the
condition for gas giant formation is independent of the metallicity.
Consequently, most of planets detected so far are thought to have been formed
by the core-accretion process, and the rest by the disk instability process.Comment: accepted for publication in The Astrophysical Journa
Indicators of Good Governance: Developing an Index of Governance Quality at the LGU Level
Governance is a complex concept. It includes the state’s institutions and structures, its decisionmaking process, its capacity to implement guidelines and the relationship between government officials and the public. Hence, this study attempts to develop a composite index of the quality of governance at the local government level. It also defines limited indicators, which can be measured consistently and can capture the substance of each dimension and their compatibility over time and space. The governance quality index constructed here is focused on three principal elements: capacity of the LGU to mobilize and utilize resources, efficiency and effectiveness of the LGU in the delivery of social services and presence of mechanism to ensure accountability.governance, local revenue, micro level accountability
Reducing reflections from mesh refinement interfaces in numerical relativity
Full interpretation of data from gravitational wave observations will require
accurate numerical simulations of source systems, particularly binary black
hole mergers. A leading approach to improving accuracy in numerical relativity
simulations of black hole systems is through fixed or adaptive mesh refinement
techniques. We describe a manifestation of numerical interface truncation error
which appears as slowly converging, artificial reflections from refinement
boundaries in a broad class of mesh refinement implementations, potentially
compromising the effectiveness of mesh refinement techniques for some numerical
relativity applications if left untreated. We elucidate this numerical effect
by presenting a model problem which exhibits the phenomenon, but which is
simple enough that its numerical error can be understood analytically. Our
analysis shows that the effect is caused by variations in finite differencing
error generated across low and high resolution regions, and that its slow
convergence is caused by the presence of dramatic speed differences among
propagation modes typical of 3+1 relativity. Lastly, we resolve the problem,
presenting a class of finite differencing stencil modifications, termed
mesh-adapted differencing (MAD), which eliminate this pathology in both our
model problem and in numerical relativity examples.Comment: 7 page
Invariance Violation Extends the Cosmic Ray Horizon ?
We postulate in the present paper that the energy-momentum relation is
modified for very high energy particles to violate Lorentz invariance and the
speed of photon is changed from the light velocity c. The violation effect is
amplified, in a sensitive way to detection, through the modified kinematical
constraints on the conservation of energy and momentum, in the absorption
process of gamma-rays colliding against photons of longer wavelengths and
converting into an electron-positron pair. For gamma-rays of energies higher
than 10 TeV, the minimum energy of the soft photons for the reaction and then
the absorption mean free path of gamma-rays are altered by orders of magnitude
from the ones conventionally estimated. Consideration is similarly applied to
high energy cosmic ray protons. The consequences may require the standard
assumptions on the maximum distance that very high energy radiation can travel
from to be revised.Comment: 14 pages, 1 figure, to be published in Ap J Letter
Spin reorientation transition in the incommensurate stripe-ordered phase of La3/2Sr1/2NiO4
The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization
measurements, and by unpolarized- and polarized-neutron diffraction. Spin
ordering with an incommensurability epsilon ~ 0.445 is observed below T_so ~ 80
K. On cooling, a spin reorientation is observed at 57 +/- 1 K, with the spin
axes rotating from 52 +/- 4 degrees to 78 +/- 3 degrees. This is the first time
a spin reorientation has been observed in a La2-xSrxNiO4+delta compound having
incommensurate stripe order.Comment: REVTex 4. 4 pages including 4 figures. Minor changes to text.
Accepted to be published in Physical Review
The accumulation and trapping of grains at planet gaps: effects of grain growth and fragmentation
We model the dust evolution in protoplanetary disks with full 3D, Smoothed
Particle Hydrodynamics (SPH), two-phase (gas+dust) hydrodynamical simulations.
The gas+dust dynamics, where aerodynamic drag leads to the vertical settling
and radial migration of grains, is consistently treated. In a previous work, we
characterized the spatial distribution of non-growing dust grains of different
sizes in a disk containing a gap-opening planet and investigated the gap's
detectability with the Atacama Large Millimeter/submillimeter Array (ALMA).
Here we take into account the effects of grain growth and fragmentation and
study their impact on the distribution of solids in the disk. We show that
rapid grain growth in the two accumulation zones around planet gaps is strongly
affected by fragmentation. We discuss the consequences for ALMA observations.Comment: Accepted for publication in Planetary and Space Science. 13 pages, 4
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