4,840 research outputs found
Color separate singlets in annihilation
We use the method of color effective Hamiltonian to study the properties of
states in which a gluonic subsystem forms a color singlet, and we will study
the possibility that such a subsystem hadronizes as a separate unit. A parton
system can normally be subdivided into singlet subsystems in many different
ways, and one problem arises from the fact that the corresponding states are
not orthogonal. We show that if only contributions of order are
included, the problem is greatly simplified. Only a very limited number of
states are possible, and we present an orthogonalization procedure for these
states. The result is simple and intuitive and could give an estimate of the
possibility to produce color separated gluonic subsystems, if no dynamical
effects are important. We also study with a simple MC the possibility that
configurations which correspond to "short strings" are dynamically favored. The
advantage of our approach over more elaborate models is its simplicity, which
makes it easier to estimate color reconnection effects in reactions which are
more complicated than the relatively simple annihilation.Comment: Revtex, 24 pages, 7 figures; Compared to the previous version, 1 new
figure is added and Monte-Carlo results are re-analyzed, as suggested by the
referee; To appear in Phys. Rev.
Matrix Transfer Function Design for Flexible Structures: An Application
The application of matrix transfer function design techniques to the problem of disturbance rejection on a flexible space structure is demonstrated. The design approach is based on parameterizing a class of stabilizing compensators for the plant and formulating the design specifications as a constrained minimization problem in terms of these parameters. The solution yields a matrix transfer function representation of the compensator. A state space realization of the compensator is constructed to investigate performance and stability on the nominal and perturbed models. The application is made to the ACOSSA (Active Control of Space Structures) optical structure
Electrodynamics of Media
Contains reports on two research projects.Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 28-043-AMC-02536(E
Electrodynamics of Media
Contains research objectives and reports on one research project.Joint Services Electronics Programs (U. S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E
Asymptotic stability, concentration, and oscillation in harmonic map heat-flow, Landau-Lifshitz, and Schroedinger maps on R^2
We consider the Landau-Lifshitz equations of ferromagnetism (including the
harmonic map heat-flow and Schroedinger flow as special cases) for degree m
equivariant maps from R^2 to S^2. If m \geq 3, we prove that near-minimal
energy solutions converge to a harmonic map as t goes to infinity (asymptotic
stability), extending previous work down to degree m = 3. Due to slow spatial
decay of the harmonic map components, a new approach is needed for m=3,
involving (among other tools) a "normal form" for the parameter dynamics, and
the 2D radial double-endpoint Strichartz estimate for Schroedinger operators
with sufficiently repulsive potentials (which may be of some independent
interest). When m=2 this asymptotic stability may fail: in the case of
heat-flow with a further symmetry restriction, we show that more exotic
asymptotics are possible, including infinite-time concentration (blow-up), and
even "eternal oscillation".Comment: 34 page
Quantum Zeno subspaces
The quantum Zeno effect is recast in terms of an adiabatic theorem when the
measurement is described as the dynamical coupling to another quantum system
that plays the role of apparatus. A few significant examples are proposed and
their practical relevance discussed. We also focus on decoherence-free
subspaces.Comment: 5 pages, 1 figure, to be published in Phys. Rev. Let
Thermal noise in half infinite mirrors with non-uniform loss: a slab of excess loss in a half infinite mirror
We calculate the thermal noise in half-infinite mirrors containing a layer of
arbitrary thickness and depth made of excessively lossy material but with the
same elastic material properties as the substrate. For the special case of a
thin lossy layer on the surface of the mirror, the excess noise scales as the
ratio of the coating loss to the substrate loss and as the ratio of the coating
thickness to the laser beam spot size. Assuming a silica substrate with a loss
function of 3x10-8 the coating loss must be less than 3x10-5 for a 6 cm spot
size and a 7 micrometers thick coating to avoid increasing the spectral density
of displacement noise by more than 10%. A similar number is obtained for
sapphire test masses.Comment: Passed LSC (internal) review. Submitted to Phys. Rev. D. (5/2001)
Replacement: Minor typo in Eq. 17 correcte
Relative "-Numerical Ranges for Applications in Quantum Control and Quantum Information
Motivated by applications in quantum information and quantum control, a new
type of "-numerical range, the relative "-numerical range denoted
, is introduced. It arises upon replacing the unitary group U(N) in
the definition of the classical "-numerical range by any of its compact and
connected subgroups .
The geometric properties of the relative "-numerical range are analysed in
detail. Counterexamples prove its geometry is more intricate than in the
classical case: e.g. is neither star-shaped nor simply-connected.
Yet, a well-known result on the rotational symmetry of the classical
"-numerical range extends to , as shown by a new approach based on
Lie theory. Furthermore, we concentrate on the subgroup , i.e. the -fold tensor product of SU(2),
which is of particular interest in applications. In this case, sufficient
conditions are derived for being a circular disc centered at
origin of the complex plane. Finally, the previous results are illustrated in
detail for .Comment: accompanying paper to math-ph/070103
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