885 research outputs found
Single-Spin Measurement and Decoherence in Magnetic Resonance Force Microscopy
We consider a simple version of a cyclic adiabatic inversion (CAI) technique
in magnetic resonance force microscopy (MRFM). We study the problem: What
component of the spin is measured in the CAI MRFM? We show that the
non-destructive detection of the cantilever vibrations provides a measurement
of the spin component along the effective magnetic field. This result is based
on numerical simulations of the Hamiltonian dynamics (the Schrodinger equation)
and the numerical solution of the master equation.Comment: 5 pages + 5 figures (PNG format
Transient Dynamics in Magnetic Force Microscopy for a Single-Spin Measurement
We analyze a single-spin measurement using a transient process in magnetic
force microscopy (MFM) which could increase the maximum operating temperature
by a factor of Q (the quality factor of the cantilever) in comparison with the
static Stern-Gerlach effect. We obtain an exact solution of the master
equation, which confirms this result. We also discuss the conditions required
to create a macroscopic Schrodinger cat state in the cantilever.Comment: 22 pages 2 figure
Recycling of textile waste by reinforcing earthy render with micro-fiber
Earth construction is worldwide spread. It is a valuable heritage to preserve because of its cultural
and socio-economical relevance. Furthermore, earth construction, since it needs significantly less
energy than modern construction techniques, and works with local materials, it contributes for
thesustainable development. In Portugal, there is an impressive earth construction heritage that
requires maintenance. Among the Portuguese traditional building techniques related to earth
construction, the rammed earth, the adobe and the tabique are the most relevant ones. This work is
focused on attempting to apply textile waste micro-fiber as an alternative sustainable reinforcement
solution of earthy render of tabique walls. Therefore, several earthy render samples reinforced with
1% textile waste micro-fiber content were prepared and mechanically tested. The main experimental
results are presented and discussed, and the main conclusions are drawn. This study also contributes
for recycling a specific waste, namely short fibers from needling machines used to produce
nonwoven fabrics
Universal asymptotic behavior in flow equations of dissipative systems
Based on two dissipative models, universal asymptotic behavior of flow
equations for Hamiltonians is found and discussed. Universal asymptotic
behavior only depends on fundamental bath properties but not on initial system
parameters, and the integro-differential equations possess an universal
attractor. The asymptotic flow of the Hamiltonian can be characterized by a
non-local differential equation which only depends on one parameter -
independent of the dissipative system or truncation scheme. Since the fixed
point Hamiltonian is trivial, the physical information is completely
transferred to the transformation of the observables. This yields a more stable
flow which is crucial for the numerical evaluation of correlation functions.
Furthermore, the low energy behavior of correlation functions is determined
analytically. The presented procedure can also be applied if relevant
perturbations are present as is demonstrated by evaluating dynamical
correlation functions for sub-Ohmic environments. It can further be generalized
to other dissipative systems.Comment: 15 pages, 9 figures; to appear in Phys. Rev.
Coulomb-gas formulation of SU(2) branes and chiral blocks
We construct boundary states in WZNW models using the bosonized
Wakimoto free-field representation and study their properties. We introduce a
Fock space representation of Ishibashi states which are coherent states of
bosons with zero-mode momenta (boundary Coulomb-gas charges) summed over
certain lattices according to Fock space resolution of . The Virasoro
invariance of the coherent states leads to families of boundary states
including the B-type D-branes found by Maldacena, Moore and Seiberg, as well as
the A-type corresponding to trivial current gluing conditions. We then use the
Coulomb-gas technique to compute exact correlation functions of WZNW primary
fields on the disk topology with A- and B-type Cardy states on the boundary. We
check that the obtained chiral blocks for A-branes are solutions of the
Knizhnik-Zamolodchikov equations.Comment: 14 pages, 3 figures, revtex4. Essentially the published versio
Wigner Distribution Function Approach to Dissipative Problems in Quantum Mechanics with emphasis on Decoherence and Measurement Theory
We first review the usefulness of the Wigner distribution functions (WDF),
associated with Lindblad and pre-master equations, for analyzing a host of
problems in Quantum Optics where dissipation plays a major role, an arena where
weak coupling and long-time approximations are valid. However, we also show
their limitations for the discussion of decoherence, which is generally a
short-time phenomenon with decay rates typically much smaller than typical
dissipative decay rates. We discuss two approaches to the problem both of which
use a quantum Langevin equation (QLE) as a starting-point: (a) use of a reduced
WDF but in the context of an exact master equation (b) use of a WDF for the
complete system corresponding to entanglement at all times
Berry's Phase in the Presence of a Stochastically Evolving Environment: A Geometric Mechanism for Energy-Level Broadening
The generic Berry phase scenario in which a two-level system is coupled to a
second system whose dynamical coordinate is slowly-varying is generalized to
allow for stochastic evolution of the slow system. The stochastic behavior is
produced by coupling the slow system to a heat resevoir which is modeled by a
bath of harmonic oscillators initially in equilibrium at temperature T, and
whose spectral density has a bandwidth which is small compared to the
energy-level spacing of the fast system. The well-known energy-level shifts
produced by Berry's phase in the fast system, in conjunction with the
stochastic motion of the slow system, leads to a broadening of the fast system
energy-levels. In the limit of strong damping and sufficiently low temperature,
we determine the degree of level-broadening analytically, and show that the
slow system dynamics satisfies a Langevin equation in which Lorentz-like and
electric-like forces appear as a consequence of geometrical effects. We also
determine the average energy-level shift produced in the fast system by this
mechanism.Comment: 29 pages, RevTex, submitted to Phys. Rev.
Exact C=1 Boundary Conformal Field Theories
We present a solution of the problem of a free massless scalar field on the
half line interacting through a periodic potential on the boundary. For a
critical value of the period, this system is a conformal field theory with a
non-trivial and explicitly calculable S-matrix for scattering from the
boundary. Unlike all other exactly solvable conformal field theories, it is
non-rational ({\it i.e.} has infinitely many primary fields). It describes the
critical behavior of a number of condensed matter systems, including
dissipative quantum mechanics and of barriers in ``quantum wires''.Comment: harvmac, 10 pages, PUPT-1432/IASSNS-HEP-93/7
Residue and residue flour from Chardonnay wine processing.
The aim of this study was to evaluate the viability of the production of the flour from the residue of production of Chardonnay white wines and characterize the change of the quality attributes during the transformation of the residue in residue flour
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