11,624 research outputs found
Lagrangian Matroids: Representations of Type
We introduce the concept of orientation for Lagrangian matroids represented
in the flag variety of maximal isotropic subspaces of dimension N in the real
vector space of dimension 2N+1. The paper continues the study started in
math.CO/0209100.Comment: Requires amssymb.sty; 17 page
Lagrangian Pairs and Lagrangian Orthogonal Matroids
Represented Coxeter matroids of types and , that is, symplectic
and orthogonal matroids arising from totally isotropic subspaces of symplectic
or (even-dimensional) orthogonal spaces, may also be represented in buildings
of type and , respectively. Indeed, the particular buildings
involved are those arising from the flags or oriflammes, respectively, of
totally isotropic subspaces. There are also buildings of type arising
from flags of totally isotropic subspaces in odd-dimensional orthogonal space.
Coxeter matroids of type are the same as those of type (since they
depend only upon the reflection group, not the root system). However, buildings
of type are distinct from those of the other types. The matroids
representable in odd dimensional orthogonal space (and therefore in the
building of type ) turn out to be a special case of symplectic (flag)
matroids, those whose top component, or Lagrangian matroid, is a union of two
Lagrangian orthogonal matroids. These two matroids are called a Lagrangian
pair, and they are the combinatorial manifestation of the ``fork'' at the top
of an oriflamme (or of the fork at the end of the Coxeter diagram of ).
Here we give a number of equivalent characterizations of Lagrangian pairs,
and prove some rather strong properties of them.Comment: Requires amssymb.sty; 12 pages, 2 LaTeX figure
Control system for hunger and its implications in animals and man
No description supplie
Simulations of disk galaxies with cosmic ray driven galactic winds
We present results from high-resolution hydrodynamic simulations of isolated
SMC- and Milky Way-sized galaxies that include a model for feedback from
galactic cosmic rays (CRs). We find that CRs are naturally able to drive winds
with mass loading factors of up to ~10 in dwarf systems. The scaling of the
mass loading factor with circular velocity between the two simulated systems is
consistent with \propto v_c^{1-2} required to reproduce the faint end of the
galaxy luminosity function. In addition, simulations with CR feedback reproduce
both the normalization and the slope of the observed trend of wind velocity
with galaxy circular velocity. We find that winds in simulations with CR
feedback exhibit qualitatively different properties compared to SN driven
winds, where most of the acceleration happens violently in situ near star
forming sites. In contrast, the CR-driven winds are accelerated gently by the
large-scale pressure gradient established by CRs diffusing from the
star-forming galaxy disk out into the halo. The CR-driven winds also exhibit
much cooler temperatures and, in the SMC-sized system, warm (T~10^4 K) gas
dominates the outflow. The prevalence of warm gas in such outflows may provide
a clue as to the origin of ubiquitous warm gas in the gaseous halos of galaxies
detected via absorption lines in quasar spectra.Comment: ApJL accepted. Replaced with accepted version. Minor revision in
response to referee comment
PRIVATIZATION AND TRANSITION ISSUES IN RUSSIAN AGRICULTURE
Agricultural and Food Policy,
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