57,017 research outputs found
Electron Capture Dissociation Mass Spectrometry of Metallo-Supramolecular Complexes
The electron capture dissociation (ECD) of metallo-supramolecular dinuclear triple-stranded helicate Fe2L3
4 ions was determined by Fourier transform ion cyclotron resonance mass spectrometry. Initial electron capture by the di-iron(II) triple helicate ions produces dinuclear double-stranded complexes analogous to those seen in solution with the monocationic metal centers CuI or AgI. The gas-phase fragmentation behavior [ECD, collision-induced dissociation (CID), and infrared multiphoton dissociation (IRMPD)] of the di-iron double-stranded complexes, (i.e., MS3 of the ECD product) was compared with the ECD, CID, and IRMPD of the CuI and AgI complexes generated from solution. The results suggest that iron-bound dimers may be of the formFeI 2L2 2 and that ECD by metallo-complexes allows access, in the gas phase,to oxidation states and coordination chemistry that cannot be accessed in solution
Velocity statistics in excited granular media
We present an experimental study of velocity statistics for a partial layer
of inelastic colliding beads driven by a vertically oscillating boundary. Over
a wide range of parameters (accelerations 3-8 times the gravitational
acceleration), the probability distribution P(v) deviates measurably from a
Gaussian for the two horizontal velocity components. It can be described by
P(v) ~ exp(-|v/v_c|^1.5), in agreement with a recent theory. The characteristic
velocity v_c is proportional to the peak velocity of the boundary. The granular
temperature, defined as the mean square particle velocity, varies with particle
density and exhibits a maximum at intermediate densities. On the other hand,
for free cooling in the absence of excitation, we find an exponential velocity
distribution. Finally, we examine the sharing of energy between particles of
different mass. The more massive particles are found to have greater kinetic
energy.Comment: 27 pages, 13 figures, to appear in Chaos, September 99, revised 3
figures and tex
Chaos in effective classical and quantum dynamics
We investigate the dynamics of classical and quantum N-component phi^4
oscillators in the presence of an external field. In the large N limit the
effective dynamics is described by two-degree-of-freedom classical Hamiltonian
systems. In the classical model we observe chaotic orbits for any value of the
external field, while in the quantum case chaos is strongly suppressed. A
simple explanation of this behaviour is found in the change in the structure of
the orbits induced by quantum corrections. Consistently with Heisenberg's
principle, quantum fluctuations are forced away from zero, removing in the
effective quantum dynamics a hyperbolic fixed point that is a major source of
chaos in the classical model.Comment: 6 pages, RevTeX, 5 figures, uses psfig, changed indroduction and
conclusions, added reference
Time evolution of the chiral phase transition during a spherical expansion
We examine the non-equilibrium time evolution of the hadronic plasma produced
in a relativistic heavy ion collision, assuming a spherical expansion into the
vacuum. We study the linear sigma model to leading order in a large-
expansion. Starting at a temperature above the phase transition, the system
expands and cools, finally settling into the broken symmetry vacuum state. We
consider the proper time evolution of the effective pion mass, the order
parameter , and the particle number distribution. We
examine several different initial conditions and look for instabilities
(exponentially growing long wavelength modes) which can lead to the formation
of disoriented chiral condensates (DCCs). We find that instabilities exist for
proper times which are less than 3 fm/c. We also show that an experimental
signature of domain growth is an increase in the low momentum spectrum of
outgoing pions when compared to an expansion in thermal equilibrium. In
comparison to particle production during a longitudinal expansion, we find that
in a spherical expansion the system reaches the ``out'' regime much faster and
more particles get produced. However the size of the unstable region, which is
related to the domain size of DCCs, is not enhanced.Comment: REVTex, 20 pages, 8 postscript figures embedded with eps
Isotropic and Anisotropic Regimes of the Field-Dependent Spin Dynamics in Sr2IrO4: Raman Scattering Studies
A major focus of experimental interest in Sr2IrO4 has been to clarify how the
magnetic excitations of this strongly spin-orbit coupled system differ from the
predictions of anisotropic 2D spin-1/2 Heisenberg model and to explore the
extent to which strong spin-orbit coupling affects the magnetic properties of
iridates. Here, we present a high-resolution inelastic light (Raman) scattering
study of the low energy magnetic excitation spectrum of Sr2IrO4 and doped
Eu-doped Sr2IrO4 as functions of both temperature and applied magnetic field.
We show that the high-field (H>1.5 T) in-plane spin dynamics of Sr2IrO4 are
isotropic and governed by the interplay between the applied field and the small
in-plane ferromagnetic spin components induced by the Dzyaloshinskii-Moriya
interaction. However, the spin dynamics of Sr2IrO4 at lower fields (H<1.5 T)
exhibit important effects associated with interlayer coupling and in-plane
anisotropy, including a spin-flop transition at Hc in Sr2IrO4 that occurs
either discontinuously or via a continuous rotation of the spins, depending
upon the in-plane orientation of the applied field. These results show that
in-plane anisotropy and interlayer coupling effects play important roles in the
low-field magnetic and dynamical properties of Sr2IrO4.Comment: 8 pages, 4 figures, submitte
Exact and approximate dynamics of the quantum mechanical O(N) model
We study a quantum dynamical system of N, O(N) symmetric, nonlinear
oscillators as a toy model to investigate the systematics of a 1/N expansion.
The closed time path (CTP) formalism melded with an expansion in 1/N is used to
derive time evolution equations valid to order 1/N (next-to-leading order). The
effective potential is also obtained to this order and its properties
areelucidated. In order to compare theoretical predictions against numerical
solutions of the time-dependent Schrodinger equation, we consider two initial
conditions consistent with O(N) symmetry, one of them a quantum roll, the other
a wave packet initially to one side of the potential minimum, whose center has
all coordinates equal. For the case of the quantum roll we map out the domain
of validity of the large-N expansion. We discuss unitarity violation in the 1/N
expansion; a well-known problem faced by moment truncation techniques. The 1/N
results, both static and dynamic, are also compared to those given by the
Hartree variational ansatz at given values of N. We conclude that late-time
behavior, where nonlinear effects are significant, is not well-described by
either approximation.Comment: 16 pages, 12 figrures, revte
Back-reaction in a cylinder
A system is studied in which initially a strong classical electric field
exists within an infinitely-long cylinder and no charges are present.
Subsequently, within the cylinder, pairs of charged particles tunnel out from
the vacuum and the current produced through their acceleration by the field
acts back on the field, setting up plasma oscillations. This yields a rough
model of phenomena that may occur in the pre-equilibrium formation phase of a
quark-gluon plasma. In an infinite volume, this back-reaction has been studied
in a field-theory description, and it has been found that the results of a full
calculation of this sort are well represented in a much simpler transport
formalism. It is the purpose here to explore that comparison for a situation
involving a cylindrical volume of given radius.Comment: 19 pages plus 13 figure
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