19,673 research outputs found
Frobenius theorem and invariants for Hamiltonian systems
We apply Frobenius integrability theorem in the search of invariants for
one-dimensional Hamiltonian systems with a time-dependent potential. We obtain
several classes of potential functions for which Frobenius theorem assures the
existence of a two-dimensional foliation to which the motion is constrained. In
particular, we derive a new infinite class of potentials for which the motion
is assurately restricted to a two-dimensional foliation. In some cases,
Frobenius theorem allows the explicit construction of an associated invariant.
It is proven the inverse result that, if an invariant is known, then it always
can be furnished by Frobenius theorem
In situ hybridization in Vitis vinifera L.
Research Not
Downregulation of Tumor Necrosis Factor Expression in the Human Mono-Mac-6 Cell Line
Mono-Mac-6 cells, but not U937 cells, can be Induced to rapidly express tumor necrosis
factor (TNF) mRNA and protein when triggered with Ilpopolysaccharlde (LPS) at 1 pg/mI.
Preincubatlon of the cells for 3 d with low amounts of LPS (10 ng/mI) results In nearly
complete suppression of TNF secretion. This downreguiatlon appears to occur at the
pretranslational level since specIfIc mRNA is virtually undetectable under these conditions.
By contrast, the same prelncubatlon with 10 ng/mI LPS results in enhanced phagocytosls
(28.6-67.2% for Staphylococcus aureus), demonstrating that not all monocyte
functions are suppressed. While these results show that only stringent exclusion of LPS
from culture media allows for Induction of TNF In the Mono-Mac-6 cell line, the pronounced
effect of LPS preincubatlon may also provide a suitable model with which to
study the mechanisms of LPS-lnduced desensitizatIon
Entanglement, fidelity and topological entropy in a quantum phase transition to topological order
We present a numerical study of a quantum phase transition from a
spin-polarized to a topologically ordered phase in a system of spin-1/2
particles on a torus. We demonstrate that this non-symmetry-breaking
topological quantum phase transition (TOQPT) is of second order. The transition
is analyzed via the ground state energy and fidelity, block entanglement,
Wilson loops, and the recently proposed topological entropy. Only the
topological entropy distinguishes the TOQPT from a standard QPT, and
remarkably, does so already for small system sizes. Thus the topological
entropy serves as a proper order parameter. We demonstrate that our conclusions
are robust under the addition of random perturbations, not only in the
topological phase, but also in the spin polarized phase and even at the
critical point.Comment: replaced with published versio
Lie symmetries for two-dimensional charged particle motion
We find the Lie point symmetries for non-relativistic two-dimensional charged
particle motion. These symmetries comprise a quasi-invariance transformation, a
time-dependent rotation, a time-dependent spatial translation and a dilation.
The associated electromagnetic fields satisfy a system of first-order linear
partial differential equations. This system is solved exactly, yielding four
classes of electromagnetic fields compatible with Lie point symmetries
Symmetries of the near horizon of a Black Hole by Group Theoretic methods
We use group theoretic methods to obtain the extended Lie point symmetries of
the quantum dynamics of a scalar particle probing the near horizon structure of
a black hole. Symmetries of the classical equations of motion for a charged
particle in the field of an inverse square potential and a monopole, in the
presence of certain model magnetic fields and potentials are also studied. Our
analysis gives the generators and Lie algebras generating the inherent
symmetries.Comment: To appear in Int. J. Mod. Phys.
Scaling Behavior of Entanglement in Two- and Three-Dimensional Free Fermions
Exactly solving a spinless fermionic system in two and three dimensions, we
investigate the scaling behavior of the block entropy in critical and
non-critical phases. The scaling of the block entropy crucially depends on the
nature of the excitation spectrum of the system and on the topology of the
Fermi surface. Noticeably, in the critical phases the scaling violates the area
law and acquires a logarithmic correction \emph{only} when a well defined Fermi
surface exists in the system. When the area law is violated, we accurately
verify a conjecture for the prefactor of the logarithmic correction, proposed
by D. Gioev and I. Klich [quant-ph/0504151].Comment: 4 pages, 4 figure
Radiation Tests for Orbiting Astronomical Observatory Scientific Report No. 1
Radiation test for orbiting astronomical observatory antenna
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