9,755 research outputs found
Performance of dynamical decoupling in bosonic environments and under pulse-timing fluctuations
We study the suppression of qubit dephasing through Uhrig dynamical
decoupling (UDD) in nontrivial environments modeled within the spin-boson
formalism. In particular, we address the case of (i) a qubit coupled to a
bosonic bath with power-law spectral density, and (ii) a qubit coupled to a
single harmonic oscillator that dissipates energy into a bosonic bath, which
embodies an example of a structured bath for the qubit. We then model the
influence of random time jitter in the UDD protocol by sorting
pulse-application times from Gaussian distributions centered at appropriate
values dictated by the optimal protocol. In case (i) we find that, when few
pulses are applied and a sharp cutoff is considered, longer coherence times and
robust UDD performances (against random timing errors) are achieved for a
super-Ohmic bath. On the other hand, when an exponential cutoff is considered a
super-Ohmic bath is undesirable. In case (ii) the best scenario is obtained for
an overdamped harmonic motion. Our study provides relevant information for the
implementation of optimized schemes for the protection of quantum states from
decoherence.Comment: 8 pages, 5 figure
Quantized spin wave modes in magnetic tunnel junction nanopillars
We present an experimental and theoretical study of the magnetic field
dependence of the mode frequency of thermally excited spin waves in rectangular
shaped nanopillars of lateral sizes 60x100, 75x150, and 105x190 nm2, patterned
from MgO-based magnetic tunnel junctions. The spin wave frequencies were
measured using spectrally resolved electrical noise measurements. In all
spectra, several independent quantized spin wave modes have been observed and
could be identified as eigenexcitations of the free layer and of the synthetic
antiferromagnet of the junction. Using a theoretical approach based on the
diagonalization of the dynamical matrix of a system of three coupled, spatially
confined magnetic layers, we have modeled the spectra for the smallest pillar
and have extracted its material parameters. The magnetization and exchange
stiffness constant of the CoFeB free layer are thereby found to be
substantially reduced compared to the corresponding thin film values. Moreover,
we could infer that the pinning of the magnetization at the lateral boundaries
must be weak. Finally, the interlayer dipolar coupling between the free layer
and the synthetic antiferromagnet causes mode anticrossings with gap openings
up to 2 GHz. At low fields and in the larger pillars, there is clear evidence
for strong non-uniformities of the layer magnetizations. In particular, at zero
field the lowest mode is not the fundamental mode, but a mode most likely
localized near the layer edges.Comment: 16 pages, 4 figures, (re)submitted to PR
The enhance of soil cation exchange capacity by using charcoal in an Typic clayey Acrothoxl in the Central Amazon - Brazil.
V1647 Ori (IRAS 05436-0007) in Outburst: the First Three Months
We report on photometric (BVRIJHK) and low dispersion spectroscopic
observations of V1647 Ori, the star that drives McNeil's Nebula, between 10
February and 7 May 2004. The star is photometrically variable atop a general
decline in brightness of about 0.3-0.4 magnitudes during these 87 days. The
spectra are featureless, aside from H-alpha and the Ca II infrared triplet in
emission, and a Na I D absorption feature. The Ca II triplet line ratios are
typical of young stellar objects. The H-alpha equivalent width may be modulated
on a period of about 60 days. The post-outburst extinction appears to be less
than 7 mag. The data are suggestive of an FU Orionis-like event, but further
monitoring will be needed to definitively characterize the outburst.Comment: Accepted for publication in the Astronomical Journa
Habilidade competitiva de sorgo (Sorghum bicolor L. Moench) em convivência com plantas de Bidens pilosa.
Efeito da aplicação pós-emergente do herbicida Halosulfuron-methyl em cultivares de sorgo sacarino e biomassa.
Phase separation methodology for physicochemical studies of soils.
A detailed study of a soil in every country is of a paramount importance, because it determines an entire economic strategy. The mineralogical properties of soils have been studied in the world for more than 100 years by various characterization techniques, X-ray diffraction being the most prominent. The main difficulty in most of employed techniques is the dominance of the majority phases in the response or the measured signal from the sample that becloud minority phases preventing their identification. The application of methods of phases'separation would provide the possibility to discern minority phases in soils. This work presents a phase separation method that employs a combination of two phenomena based on principles of fluid dynamics: flotation and sedimentation. Different characterization methods were used to analyse the produced soil samples. The methodology employed for separation of phases allowed the complete separation of clay phase from heavier mineral phases. This result makes it possible to discern minority mineral phases of soils that are difficult to detect. A more accurate determination of the mineralogical composition of a soil becomes feasible
Características químicas e estoque de carbono dos solos sob diferentes coberturas vegetais e em sistemas tradicionais de uso da terra na região do Alto Solimões - Amazonas.
As atividades humanas transformam os ambientes naturais com diferentes intensidades de manejo e uso do solo. Com o objetivo de verificar as alterações causadas nos solos pelo manejo realizado por agricultores da região, foram feitas seis grades amostrais (janelas), com cento e um pontos ao todo, contendo os sistemas de uso da terra: floresta primária (FP), floresta secundária (FS > sete anos), florestas secundárias (CAP < sete anos), sistemas agroflorestais (SAF?s), roças (RÇ) e pastagens (PAS), no município de Benjamin Constant
On rigidly rotating perfect fluid cylinders
The gravitational field of a rigidly rotating perfect fluid cylinder with
gamma- law equation of state is found analytically. The solution has two
parameters and is physically realistic for gamma in the interval (1.41,2].
Closed timelike curves always appear at large distances.Comment: 10 pages, Revtex (galley
O aumento da capacidade de troca de cátions (CTC) do solo através da aplicação de carvão vegetal em um Latossolo Amarelo na Amazônia Central.
O objetivo deste trabalho foi avaliar o efeito da aplicação de doses de carvão vegetal na CTC de um Latossolo Amarelo cultivado com bananeira
- …