48,695 research outputs found
Explaining the Great Moderation: it is not the shocks
This paper shows that the explanation of the decline in the volatility of GDP growth since the mid-eighties is not the decline in the volatility of exogenous shocks but rather a change in their propagation mechanism. JEL Classification: E32, E37, C32, C53Great Moderation, Information, shocks
Coordinated cadastral system for Peninsular Malaysia : from concept to reality
The main objectives of conducting cadastral surveys that had been promulgated in the early days of its practice have since been continually adhered to and later came to be adopted as amongst the principal functions of DSMM. They were stated in the Survey Regulations (DSMM, 1976) as follows: â(a) To provide evidence which will completely and permanently identify the land conveyed by any title issued by government. (b) To compile and make available records of alienation necessary for intelligent land administration.
Acoustic fluidization for earthquakes?
Melosh [1996] has suggested that acoustic fluidization could provide an
alternative to theories that are invoked as explanations for why some crustal
faults appear to be weak. We show that there is a subtle but profound
inconsistency in the theory that unfortunately invalidates the results. We
propose possible remedies but must acknowledge that the relevance of acoustic
fluidization remains an open question.Comment: 13 page
Transient events in bright debris discs: Collisional avalanches revisited
A collisional avalanche is set off by the breakup of a large planetesimal,
releasing small unbound grains that enter a debris disc located further away
from the star, triggering there a collisional chain reaction that can
potentially create detectable transient structures. We explore this mechanism,
using for the first time a code coupling dynamical and collisional evolutions,
and investigate if avalanches could explain the short-term luminosity
variations observed in some extremely bright discs. We consider two set-ups: a
cold disc case, with a dust release at 10au and an outer disc extending from 50
to 120au, and a warm disc case with the release at 1au and a 5-12au outer disc.
We find that avalanches could leave detectable structures on resolved images,
for both cold and warm disc cases, in discs with optical depth of a few
, provided that large dust masses
(10-510g) are initially released. The integrated
photometric excess due to an avalanche is limited, less than 10% for these
released dust masses, peaking in the mid-IR and becoming insignificant beyond
40-50m. Contrary to earlier studies, we do not obtain stronger
avalanches when increasing to higher values. Likewise, we do not observe
a significant luminosity deficit, as compared to the pre-avalanche level, after
the passage of the avalanche. These two results concur to make avalanches an
unlikely explanation for the sharp luminosity drops observed in some extremely
bright debris discs. The ideal configuration for observing an avalanche would
be a two-belt structure, with an inner belt of fractional luminosity >10
where breakups of massive planetesimals occur, and a more massive outer belt,
with of a few , into which the avalanche chain reaction
develops and propagates.Comment: Accepted for publication in Astronomy & Astrophysics (abstract
drastically shortened to meet astro-ph requirements
Large Scale Structure and Cosmic Rays revisited
We investigate the possibility that ultra high energy cosmic rays (E > 10^19
eV) are related to the distribution of matter on large scales. The large scale
structure (LSS) data stems from the recent IRAS PSCz redshift survey. We
present preliminary predictions drawn from an anisotropic distribution of
sources which follows the galaxy distribution.Comment: 6 pages, 2 figures, uses World Scientific style. To appear in the
proceedings of "Third International Workshop on New Worlds in Astro-Particle
Physics", 1-3 Set. 2000, Faro, Portugal and X ENAA, 27-28 Jul. 2000, Lisbon,
Portuga
The Galactic halo magnetic field revisited
Recently, Sun et al. (2008) published new Galactic 3D-models of magnetic
fields in the disk and halo of the Milky Way and the distribution of cosmic-ray
electron density by taking into account the thermal electron density model
NE2001 by Cordes & Lazio (2002, 2003). The models successfully reproduce
observed continuum and polarization all-sky maps and the distribution of
rotation measures of extragalactic sources across the sky. However, the model
parameters obtained for the Galactic halo, although reproducing the
observations, seem physically unreasonable: the magnetic field needs to be
significantly stronger in the Galactic halo than in the plane and the
cosmic-ray distribution must be truncated at about 1 kpc to avoid excessive
synchrotron emission from the halo. The reason for these unrealistic parameters
was the low scale-height of the warm thermal gas of about 1 kpc adapted in the
NE2001 model. However, this scale-height seemed well settled by numerous
investigations. Recently, the scale-height of the warm gas in the Galaxy was
revised by Gaensler et al. (2008) to about 1.8 kpc, by showing that the 1 kpc
scale-height results from a systematic bias in the analysis of pulsar data.
This implies a higher thermal electron density in the Galactic halo, which in
turn reduces the halo magnetic field strength to account for the observed
rotation measures of extragalactic sources. We slightly modified the NE2001
model for the new scale-height and revised the Sun et al. (2008) model
parameters accordingly: the strength of the regular halo magnetic field is now
2 microG or lower, and the physically unrealistic cutoff in z for the
cosmic-ray electron density is removed. The simulations based on the revised
3D-models reproduce all-sky observations as before.Comment: 11 pages, 6 figures, accepted for publication in Research in
Astronomy and Astrophysics (RAA
Propagation Speed of the Maximum of the Fundamental Solution to the Fractional Diffusion-Wave Equation
In this paper, the one-dimensional time-fractional diffusion-wave equation
with the fractional derivative of order is revisited. This
equation interpolates between the diffusion and the wave equations that behave
quite differently regarding their response to a localized disturbance: whereas
the diffusion equation describes a process, where a disturbance spreads
infinitely fast, the propagation speed of the disturbance is a constant for the
wave equation. For the time fractional diffusion-wave equation, the propagation
speed of a disturbance is infinite, but its fundamental solution possesses a
maximum that disperses with a finite speed. In this paper, the fundamental
solution of the Cauchy problem for the time-fractional diffusion-wave equation,
its maximum location, maximum value, and other important characteristics are
investigated in detail. To illustrate analytical formulas, results of numerical
calculations and plots are presented. Numerical algorithms and programs used to
produce plots are discussed.Comment: 22 pages 6 figures. This paper has been presented by F. Mainardi at
the International Workshop: Fractional Differentiation and its Applications
(FDA12) Hohai University, Nanjing, China, 14-17 May 201
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