3,153 research outputs found
Preparation and mechanical properties of machinable alumina/mica composites
ArticleJOURNAL OF THE EUROPEAN CERAMIC SOCIETY. 26(9): 1687 -1693 (2006)journal articl
REUSE OF WASTEWATER FROM POLYESTER FIBRES DYEING PROCESS BY THERMAL FIXATION WITH DYE ACID BASE: CASE STUDY IN A BRAZILIAN AUTO PARTS FACILITY
This work aims to test biodegradable chemicals into treatment of textile waste water from an auto parts facility with goal of reuse of water treated in dyeing process of lace used in safety belts. It presents a method that suits the treatment of waste water with local environmental regulations and allows the reuse of water through the adoption of actions that replace the conventional physical-chemical treatment by biodegradable products, which naturally extend the possibility of reuse beyond the process and increase the quality of water for reuse in that one, allowing satisfy the requirements of product quality demanded by the market. This work proposes substitution of some chemicals by biodegradable products and comparison to previous results obtained with current treatment for the same conditions preestablished. Also the ultra-filtration method had evaluated and its results were compared to traditional process and to new proposal. According to results obtained, replacement of traditional chemicals by biodegradable products is technical and economical viable and attends to the waste water reuse policy proposed
Transient current spectroscopy of a quantum dot in the Coulomb blockade regime
Transient current spectroscopy is proposed and demonstrated in order to
investigate the energy relaxation inside a quantum dot in the Coulomb blockade
regime. We employ a fast pulse signal to excite an AlGaAs/GaAs quantum dot to
an excited state, and analyze the non-equilibrium transient current as a
function of the pulse length. The amplitude and time-constant of the transient
current are sensitive to the ground and excited spin states. We find that the
spin relaxation time is longer than, at least, a few microsecond.Comment: 5 pages, 3 figure
Dephasing of coupled spin qubit system during gate operations due to background charge fluctuations
It has been proposed that a quantum computer can be constructed based on
electron spins in quantum dots or based on a superconducting nanocircuit.
During two-qubit operations, the fluctuation of the coupling parameters is a
critical factor. One source of such fluctuation is the stirring of the
background charges. We focused on the influence of this fluctuation on a
coupled spin qubit system. The induced fluctuation in exchange coupling changes
the amount of entanglement, fidelity, and purity. In our previous study, the
background charge fluctuations were found to be an important channel of
dephasing for a single Josephson qubit.Comment: 10 pages, 7 figure. to be publishe
Universal oscillations in counting statistics
Noise is a result of stochastic processes that originate from quantum or
classical sources. Higher-order cumulants of the probability distribution
underlying the stochastic events are believed to contain details that
characterize the correlations within a given noise source and its interaction
with the environment, but they are often difficult to measure. Here we report
measurements of the transient cumulants > of the number n of passed
charges to very high orders (up to m=15) for electron transport through a
quantum dot. For large m, the cumulants display striking oscillations as
functions of measurement time with magnitudes that grow factorially with m.
Using mathematical properties of high-order derivatives in the complex plane we
show that the oscillations of the cumulants in fact constitute a universal
phenomenon, appearing as functions of almost any parameter, including time in
the transient regime. These ubiquitous oscillations and the factorial growth
are system-independent and our theory provides a unified interpretation of
previous theoretical studies of high-order cumulants as well as our new
experimental data.Comment: 19 pages, 4 figures, final version as published in PNA
Spins in few-electron quantum dots
This review describes the physics of spins in quantum dots containing one or
two electrons, from an experimentalist's viewpoint. Various methods for
extracting spin properties from experiment are presented, restricted
exclusively to electrical measurements. Furthermore, experimental techniques
are discussed that allow for: (1) the rotation of an electron spin into a
superposition of up and down, (2) the measurement of the quantum state of an
individual spin and (3) the control of the interaction between two neighbouring
spins by the Heisenberg exchange interaction. Finally, the physics of the
relevant relaxation and dephasing mechanisms is reviewed and experimental
results are compared with theories for spin-orbit and hyperfine interactions.
All these subjects are directly relevant for the fields of quantum information
processing and spintronics with single spins (i.e. single-spintronics).Comment: final version (52 pages, 49 figures), Rev. Mod. Phy
Superposition of photon- and phonon- assisted tunneling in coupled quantum dots
We report on electron transport through an artificial molecule formed by two
tunnel coupled quantum dots, which are laterally confined in a two-dimensional
electron system of an AlGaAs/GaAs heterostructure. Coherent
molecular states in the coupled dots are probed by photon-assisted tunneling
(PAT). Above 10 GHz, we observe clear PAT as a result of the resonance between
the microwave photons and the molecular states. Below 8 GHz, a pronounced
superposition of phonon- and photon-assisted tunneling is observed. Coherent
superposition of molecular states persists under excitation of acoustic
phonons.Comment: 5 pages, 4 figure
Electron transport through double quantum dots
Electron transport experiments on two lateral quantum dots coupled in series
are reviewed. An introduction to the charge stability diagram is given in terms
of the electrochemical potentials of both dots. Resonant tunneling experiments
show that the double dot geometry allows for an accurate determination of the
intrinsic lifetime of discrete energy states in quantum dots. The evolution of
discrete energy levels in magnetic field is studied. The resolution allows to
resolve avoided crossings in the spectrum of a quantum dot. With microwave
spectroscopy it is possible to probe the transition from ionic bonding (for
weak inter-dot tunnel coupling) to covalent bonding (for strong inter-dot
tunnel coupling) in a double dot artificial molecule. This review on the
present experimental status of double quantum dot studies is motivated by their
relevance for realizing solid state quantum bits.Comment: 32 pages, 31 figure
Photon-Assisted Transport Through Ultrasmall Quantum Dots: Influence of Intradot Transitions
We study transport through one or two ultrasmall quantum dots with discrete
energy levels to which a time-dependent field is applied (e.g., microwaves).
The AC field causes photon-assisted tunneling and also transitions between
discrete energy levels of the dot. We treat the problem by introducing a
generalization of the rotating-wave approximation to arbitrarily many levels.
We calculate the dc-current through one dot and find satisfactory agreement
with recent experiments by Oosterkamp et al. . In addition, we propose a novel
electron pump consisting of two serially coupled single-level quantum dots with
a time-dependent interdot barrier.Comment: 16 pages, Revtex, 10 eps-figure
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