20,948 research outputs found
Coronal mass ejections, magnetic clouds, and relativistic magnetospheric electron events: ISTP
The role of high-speed solar wind streams in driving relativistic electron acceleration within the Earth\u27s magnetosphere during solar activity minimum conditions has been well documented. The rising phase of the new solar activity cycle (cycle 23) commenced in 1996, and there have recently been a number of coronal mass ejections (CMEs) and related âmagnetic cloudsâ at 1 AU. As these CME/cloud systems interact with the Earth\u27s magnetosphere, some events produce substantial enhancements in the magnetospheric energetic particle population while others do not. This paper compares and contrasts relativistic electron signatures observed by the POLAR, SAMPEX, Highly Elliptical Orbit, and geostationary orbit spacecraft during two magnetic cloud events: May 27â29, 1996, and January 10â11, 1997. Sequences were observed in each case in which the interplanetary magnetic field was first strongly southward and then rotated northward. In both cases, there were large solar wind density enhancements toward the end of the cloud passage at 1 AU. Strong energetic electron acceleration was observed in the January event, but not in the May event. The relative geoeffectiveness for these two cases is assessed, and it is concluded that large induced electric fields (âB/ât) caused in situ acceleration of electrons throughout the outer radiation zone during the January 1997 event
Capture zones of the family of functions lambda z^m exp(z)
We consider the family of entire transcendental maps given by where m>=2. All functions have a
superattracting fixed point at z=0, and a critical point at z=-m. In the
dynamical plane we study the topology of the basin of attraction of z=0. In the
parameter plane we focus on the capture behaviour, i.e., \lambda values such
that the critical point belongs to the basin of attraction of z=0. In
particular, we find a capture zone for which this basin has a unique connected
component, whose boundary is then non-locally connected. However, there are
parameter values for which the boundary of the immediate basin of z=0 is a
quasicircle.Comment: 25 pages, 14 figures. Accepted for publication in the International
Journal of bifurcation and Chao
A study of the temperature dependence of bienzyme systems and enzymatic chains
It is known that most enzyme-facilitated reactions are highly temperature dependent processes. In general, the temperature coefficient, Q10, of a simple reaction reaches 2.0-3.0. Nevertheless, some enzyme-controlled processes have much lower Q10 (about 1.0), which implies that the process is almost temperature independent, even if individual reactions involved in the process are themselves highly temperature dependent. In this work, we investigate a possible mechanism for this apparent temperature compensation: simple mathematical models are used to study how varying types of enzyme reactions are affected by temperature. We show that some bienzyme-controlled processes may be almost temperature independent if the modules involved in the reaction have similar temperature dependencies, even if individually, these modules are strongly temperature dependent. Further, we show that in non-reversible enzyme chains the stationary concentrations of metabolites are dependent only on the relationship between the temperature dependencies of the first and last modules, whilst in reversible reactions, there is a dependence on every module. Our findings suggest a mechanism by which the metabolic processes taking place within living organisms may be regulated, despite strong variation in temperature
Bose-Einstein-condensed systems in random potentials
The properties of systems with Bose-Einstein condensate in external
time-independent random potentials are investigated in the frame of a
self-consistent stochastic mean-field approximation. General considerations are
presented, which are valid for finite temperatures, arbitrary strengths of the
interaction potential, and for arbitrarily strong disorder potentials. The
special case of a spatially uncorrelated random field is then treated in more
detail. It is shown that the system consists of three components, condensed
particles, uncondensed particles and a glassy density fraction, but that the
pure Bose glass phase with only a glassy density does not appear. The theory
predicts a first-order phase transition for increasing disorder parameter,
where the condensate fraction and the superfluid fraction simultaneously jump
to zero. The influence of disorder on the ground-state energy, the stability
conditions, the compressibility, the structure factor, and the sound velocity
are analyzed. The uniform ideal condensed gas is shown to be always
stochastically unstable, in the sense that an infinitesimally weak disorder
destroys the Bose-Einstein condensate, returning the system to the normal
state. But the uniform Bose-condensed system with finite repulsive interactions
becomes stochastically stable and exists in a finite interval of the disorder
parameter.Comment: Latex file, final published varian
Thermodynamics of low dimensional spin-1/2 Heisenberg ferromagnets in an external magnetic field within Green function formalism
The thermodynamics of low dimensional spin-1/2 Heisenberg ferromagnets (HFM)
in an external magnetic field is investigated within a second-order two-time
Green function formalism in the wide temperature and field range. A crucial
point of the proposed scheme is a proper account of the analytical properties
for the approximate transverse commutator Green function obtained as a result
of the decoupling procedure. A good quantitative description of the correlation
functions, magnetization, susceptibility, and heat capacity of the HFM on a
chain, square and triangular lattices is found for both infinite and
finite-sized systems. The dependences of the thermodynamic functions of 2D HFM
on the cluster size are studied. The obtained results agree well with the
corresponding data found by Bethe ansatz, exact diagonalization, high
temperature series expansions, and quantum Monte Carlo simulations.Comment: 11 pages, 14 figure
The running coupling from the four-gluon vertex in Landau gauge Yang-Mills theory
We consider the running coupling from the four-gluon vertex in Landau gauge,
SU() Yang-Mills theory as given by a combination of dressing functions of
the vertex and the gluon propagator. We determine these functions numerically
from a coupled set of Dyson-Schwinger equations. We reproduce asymptotic
freedom in the ultraviolet momentum region and find a coupling of order one at
mid-momenta. In the infrared we find a nontrivial (i.e. nonzero) fixed point
which is three orders of magnitude smaller than the corresponding fixed point
in the coupling of the ghost-gluon vertex. This result explains why the
Dyson-Schwinger and the functional renormalization group equations for the two
point functions can agree in the infrared, although their structure is quite
different. Our findings also support Zwanziger's notion of an infrared
effective theory driven by the Faddeev-Popov determinant.Comment: 25 pages, 4 figures; v2: minor clarifications added and typos
corrected, version accepted by PR
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