37,319 research outputs found
Impact of Solar Wind Depression on the Dayside Magnetosphere under Northward Interplanetary Magnetic Field
We present a follow up study of the sensitivity of the Earth's magnetosphere
to solar wind activity using a particles-in-cell model [Baraka and Ben Jaffel,
2007], but here during northward IMF. The formation of the magnetospheric
cavity and its elongation is obtained with the classical structure of a
magnetosphere with parallel lobes. An impulsive disturbance is then applied to
the system by changing the bulk velocity of the solar wind to simulate a
decrease in the solar wind dynamic pressure followed by its recovery. In
response to the imposed disturbance, a gap [abrupt depression] in the incoming
solar wind plasma appears moving toward the Earth. The gap's size is a ~15 RE
and is comparable to the sizes previously obtained for both Bz<0 and Bz =0.
During the initial phase of the disturbance, the dayside magnetopause (MP)
expands slower than the previous cases of IMF orientations as a result of the
depression. The size of the MP expands nonlinearly due to strengthening of its
outer boundary by the northward IMF. Also, during the initial 100 {\Delta}t,
the MP shrank down from 13.3 RE to ~9.2 RE before it started expanding; a
phenomenon that was also observed for southern IMF conditions but not during
the no IMF case. As soon as they felt the solar wind depression, cusps widened
at high altitude while dragged in an upright position. For the field's
topology, the reconnection between magnetospheric and magnetosheath fields is
clearly observed in both northward and southward cusps areas. Also, the tail
region in the northward IMF condition is more confined, in contrast to the
fishtail-shape obtained in the southward IMF case. An X-point is formed in the
tail at ~110 RE compared to ~103 RE and ~80 RE for Bz =0 and Bz <0
respectively. Our findings are consistent with existing reports from many space
observatories for which predictions are proposed to test furthermore our
simulation technique.Comment: 48 pages, 6 figures, 1 table, accepted for publication in Annales
Geophysicae (ANGEO Communicates
Banking in General Equilibrium
This paper attempts to provide a step towards understanding the role of financial intermediaries ("banks") in aggregate economic activity. We first develop a model of the intermediary sector which is highly simplified, but rich enough to motivate several special features of bauks. Of particular importance in our model is the assumption that banks are more efficient than the public in evaluating and auditing certain information --intensive loan projects. Banks are also assumed to have private information about their investments, which motivates the heavy reliance of banks on debt rather than equity finance and their need for buffer stock capital. We embed this intermediary sector in a general equilibrium framework, which includes consumers and a non-banking investment sector. Mainly because banks have superior access to some investments, factors affecting the size or efficiency of banking will also have an impact on the aggregate economy. Among the factors affecting intermediation, we show, are the adequacy of bank capital, the riskiness of bank investments, and the costs of bank monitoring. We also show that our model is potentially useful for understanding the macroeconomic effects of phenomena such as financial crises, disintermediation, banking regulation, and certain types of monetary policy.
The Cyclical Behavior of Industrial Labor Markets: A Comparison of the Pre-War and Post-War Eras
This paper studies the cyclical behavior of a number of industrial labor markets of the pre-war (1923-1939) and post-war (1954-1982) eras. In the spirit of Burns and Mitchell we do not test a specific structural model of the labor market but instead concentrate on describing the qualitative features of the (monthly, industry-level) data.The two principal questions we ask are: First, how is labor input (as measured by the number of workers, the hours of work, and the intensity of utilization) varied over the cycle ? Second, what is the cyclical behaviorof labor compensation (as measured by real wages, product wages, and real weekly earnings) ? We study these questions in both the frequency domain and the time domain. Many of our findings simply reinforce, or perhaps refine, existing perceptions of cyclical labor market behavior. However, we do find some interesting differences between the pre-war and the post-war periods in ther elative use of layoffs and short hours in downturns, and in the cyclical behavior of the real wage.
Percolation with Multiple Giant Clusters
We study the evolution of percolation with freezing. Specifically, we
consider cluster formation via two competing processes: irreversible
aggregation and freezing. We find that when the freezing rate exceeds a certain
threshold, the percolation transition is suppressed. Below this threshold, the
system undergoes a series of percolation transitions with multiple giant
clusters ("gels") formed. Giant clusters are not self-averaging as their total
number and their sizes fluctuate from realization to realization. The size
distribution F_k, of frozen clusters of size k, has a universal tail, F_k ~
k^{-3}. We propose freezing as a practical mechanism for controlling the gel
size.Comment: 4 pages, 3 figure
Gravitational energy as dark energy: Concordance of cosmological tests
We provide preliminary quantitative evidence that a new solution to averaging
the observed inhomogeneous structure of matter in the universe [gr-qc/0702082,
arxiv:0709.0732], may lead to an observationally viable cosmology without
exotic dark energy. We find parameters which simultaneously satisfy three
independent tests: the match to the angular scale of the sound horizon detected
in the cosmic microwave background anisotropy spectrum; the effective comoving
baryon acoustic oscillation scale detected in galaxy clustering statistics; and
type Ia supernova luminosity distances. Independently of the supernova data,
concordance is obtained for a value of the Hubble constant which agrees with
the measurement of the Hubble Key team of Sandage et al [astro-ph/0603647].
Best-fit parameters include a global average Hubble constant H_0 = 61.7
(+1.2/-1.1) km/s/Mpc, a present epoch void volume fraction of f_{v0} = 0.76
(+0.12/-0.09), and an age of the universe of 14.7 (+0.7/-0.5) billion years as
measured by observers in galaxies. The mass ratio of non-baryonic dark matter
to baryonic matter is 3.1 (+2.5/-2.4), computed with a baryon-to-photon ratio
that concords with primordial lithium abundances.Comment: 4 pages, 2 figures; v2 improved statistics, references added, to
appear in ApJ Letter
Panel discussion: inflation targeting
Monetary policy ; Banks and banking, Central ; European Central Bank
Generalizations of the Abstract Boundary singularity theorem
The Abstract Boundary singularity theorem was first proven by Ashley and
Scott. It links the existence of incomplete causal geodesics in strongly
causal, maximally extended spacetimes to the existence of Abstract Boundary
essential singularities, i.e., non-removable singular boundary points. We give
two generalizations of this theorem: the first to continuous causal curves and
the distinguishing condition, the second to locally Lipschitz curves in
manifolds such that no inextendible locally Lipschitz curve is totally
imprisoned. To do this we extend generalized affine parameters from
curves to locally Lipschitz curves.Comment: 24 page
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