19,183 research outputs found
Reversible current control apparatus Patent
Reversible current directing circuitry for reversible motor contro
Dynamics of fingering convection II: The formation of thermohaline staircases
Regions of the ocean's thermocline unstable to salt fingering are often
observed to host thermohaline staircases, stacks of deep well-mixed convective
layers separated by thin stably-stratified interfaces. Decades after their
discovery, however, their origin remains controversial. In this paper we use 3D
direct numerical simulations to shed light on the problem. We study the
evolution of an analogous double-diffusive system, starting from an initial
statistically homogeneous fingering state and find that it spontaneously
transforms into a layered state. By analysing our results in the light of the
mean-field theory developed in Paper I, a clear picture of the sequence of
events resulting in the staircase formation emerges. A collective instability
of homogeneous fingering convection first excites a field of gravity waves,
with a well-defined vertical wavelength. However, the waves saturate early
through regular but localized breaking events, and are not directly responsible
for the formation of the staircase. Meanwhile, slower-growing, horizontally
invariant but vertically quasi-periodic gamma-modes are also excited and grow
according to the gamma-instability mechanism. Our results suggest that the
nonlinear interaction between these various mean-field modes of instability
leads to the selection of one particular gamma-mode as the staircase
progenitor. Upon reaching a critical amplitude, this progenitor overturns into
a fully-formed staircase. We conclude by extending the results of our
simulations to real oceanic parameter values, and find that the progenitor
gamma-mode is expected to grow on a timescale of a few hours, and leads to the
formation of a thermohaline staircase in about one day with an initial spacing
of the order of one to two metres.Comment: 18 pages, 9 figures, associated mpeg file at
http://earth.uni-muenster.de/~stellma/movie_small.mp4, submitted to JF
Spitzer Observations of High Redshift Radio Galaxies
We present the results of a comprehensive Spitzer survey of 70 radio galaxies
across 1<z<5.2. Using IRAC, IRS and MIPS imaging we determine the rest-frame
AGN contribution to the stellar emission peak at 1.6um. The stellar
luminosities are found to be consistent with that of a giant elliptical with a
stellar mass of 10^11-12Msun. The mean stellar mass remains constant at
\~10^11.5Msun up to z=3 indicating that the upper end of the mass function is
already in place by this redshift. The mid-IR luminosities imply bolometric IR
luminosities that would classify all sources as ULIRGs. The mid-IR to radio
luminosity generally correlate implying a common origin for these emissions.
The ratio is higher than that found for lower redshift, ie z<1, radio galaxies.Comment: 6 pages, 5 figures, to appear in the proceedings of "The Spitzer
Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution",
held in Pasadena, November 200
Promoting an Effective Market Economy in a Changing World
In this paper we examine the main challenges in promoting an effective market economy. While the paper ranges widely across the spectrum of economic institutions and policies, the central theme is the importance of macroeconomic stability for economic growth in the medium and long run. Macroeconomic stability may be seen as a public good. Its provision is among the essential responsibilities of the state both in modern market economies and in economies transforming themselves into modern market economies. Following this brief introduction, Section II considers four key aspects of the economic environment of the coming decade: increasing internationalisation; market-orientation; diminished government role; high real interest rates. Section III reviews the reasons why macroeconomic stability matters for economic performance and summarises the key empirical evidence supporting the existence of a causal link. Section IV deals with the design of domestic and international policies and institutions to promote macroeconomic stability and Section V asks how national governments and international institutions can take advantage of the current relatively stable global macroeconomic environment to improve medium-term growth. Section IV concludes. While our discussion will range broadly both theoretically and empirically, we shall emphasise lessons for , and experience from, countries attempting to create a market economy.
Planetary magnetospheres
A concise overview is presented of our understanding of planetary magnetospheres (and in particular, of that of the Earth), as of the end of 1981. Emphasis is placed on processes of astrophysical interest, e.g., on particle acceleration, collision-free shocks, particle motion, parallel electric fields, magnetic merging, substorms, and large scale plasma flows. The general morphology and topology of the Earth's magnetosphere are discussed, and important results are given about the magnetospheres of Jupiter, Saturn and Mercury, including those derived from the Voyager 1 and 2 missions and those related to Jupiter's satellite Io. About 160 references are cited, including many reviews from which additional details can be obtained
Analysis and interpretation of new low-energy Pi-Pi scattering data
The recently published E865 data on charged K_e4 decays and Pi-Pi phases are
reanalyzed to extract values of the two S-wave scattering lengths, of the
subthreshold parameters alpha and beta, of the low-energy constants l3-bar and
l4-bar as well as of the main two-flavour order parameters: and F_pi
in the limit m_u = m_d = 0 taken at the physical value of the strange quark
mass. Our analysis is exclusively based on direct experimental information on
Pi-Pi phases below 800 MeV and on the new solutions of the Roy equations by
Ananthanarayan et al. The result is compared with the theoretical prediction
relating 2 a_0^0 - 5 a_0^2 and the scalar radius of the pion, which was
obtained in two-loop Chiral Perturbation Theory. A discrepancy at the 1-sigma
level is found and commented upon.Comment: Published version, to appear in Eur. Phys. J.
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