1,747 research outputs found
Quantum dynamics in single spin measurement
We study the quantum dynamics of a model for the single-spin measurement in
magnetic-resonance force microscopy. We consider an oscillating driven
cantilever coupled with the magnetic moment of the sample. Then, the cantilever
is damped through an external bath and its readout is provided by a radiation
field. Conditions for reliable measurements will be discussed.Comment: 7 pages, 3 figure
Macroscopic Quantum Tunneling of a Domain Wall in a Ferromagnetic Metal
The macroscopic quantum tunneling of a planar domain wall in a ferromagnetic
metal is studied based on the Hubbard model. It is found that the ohmic
dissipation is present even at zero temperature due to the gapless Stoner
excitation, which is the crucial difference from the case of the insulating
magnet. The dissipative effect is calculated as a function of width of the wall
and is shown to be effective in a thin wall and in a weak ferromagnet. The
results are discussed in the light of recent experiments on ferromagnets with
strong anisotropy. PACS numbers:75.60.Ch, 03.65.Sq, 75.10.LpComment: 13page
Tentativas de Suicídio em Adolescentes Internados na Unidade de Internamento de Pedopsiquiatria do Centro Hospitalar de Lisboa Central (CHLC) :Janeiro de 2006 a Fevereiro de 2009
Micropropagation of a recalcitrant pine (Pinus pinea L.): An overview of the effects of ectomycorrhizal inoculation
Stone pine (Pinus pinea L.) is an economically important forest species in some regions of Iberian Peninsula. Portugal and Spain have nearly 500,000 ha of stone pine stands, representing 85% of worldwide distribution. The main use of this species is for the production of seeds (pinion) for food industry. In addition to its enormous profitability as a producer of seeds, it has beneficial impact on soil protection, dunes fixation and is a pioneer species particularly for cork and holm oaks degraded ecosystems. Stone pine plantations are today a major source of income for forestry holdings. Investments have targeted breeding, reforestation, forest management and harvesting. The maternal inheritance of desirable characteristics such as cone weight, number of seeds per cone and seed length is considerably high in this species thus encouraging the selection of seeds from “plus” trees. The selected trees have been propagated by grafting and micropropagation. However, grafting generates high variability due to scion-rootstock interaction that varies production levels. The production of clonal plants from selected seeds by micropropagation techniques has advanced very slowly due to the recalcitrance of this species in tissue culture and particularly to adventitious rooting of microshoots. Due to the tremendous importance of developing a reproducible tissue culture method for clonal propagation, a study has been carried out for over a decade to enhance rooting and acclimation. During this period of time, continuous increments in the multiplication rate and rooting frequency were achieved by introducing variations in culture media composition and conditions. Auxins, carbohydrates, light quality and duration, temperature at different concentrations and levels as well as compounds such as coumarin; salicylic acid, polyamines, etc. were tested for induction and expression phases of adventitious rooting. Despite these efforts, microshoots regenerated through organogenesis from mature embryo cotyledons failed to root or to have sustained root growth. At this point, an in vitro co-culture technique of stone pine microshoots with ectomycorrhizal-fungi was introduced to overcome the adventitious root growth cessation in vitro and improve root development during acclimation phase. An overview of the results showing the positive effect of fungal inoculation in promoting root growth in vitro and on plantlet survival during acclimation will be presented. Preliminary results of biochemical signals between Pinus pinea/Pisolithus arhizus during early steps of in vitro culture detected by liquid chromatography-mass spectrometry that might be responsible for the positive effect on root growth will be also presented
Atividade da urease e da arginase em solo de cerrado adicionado a pó de ardósia e cultivado com milho.
Localization on short-range potentials in dissipative quantum mechanics
In this Letter the problem of the existence of a state localized on a weak
short-range attractive potential in the presence of dissipation is considered.
It is shown that, contrary to the pure quantum case, a localized state is
produced in any number of dimensions, while in low dimensions dissipation leads
to much stronger localization. The results have physical implications for the
dissipative dynamics of objects such as heavy particles in Fermi liquids and
for superconductivity in high- materials.Comment: RevTeX, 4 pages, 1 figure. Published versio
Quantum master equation descriptions of a nanomechanical resonator coupled to a single-electron transistor
We analyse the quantum dynamics of a nanomechanical resonator coupled to a
normal-state single-electron transistor (SET). Starting from a microscopic
description of the system, we derive a master equation for the SET island
charge and resonator which is valid in the limit of weak electro-mechanical
coupling. Using this master equation we show that, apart from brief transients,
the resonator always behaves like a damped harmonic oscillator with a shifted
frequency and relaxes into a thermal-like steady state. Although the behaviour
remains qualitatively the same, we find that the magnitude of the resonator
damping rate and frequency shift depend very sensitively on the relative
magnitudes of the resonator period and the electron tunnelling time. Maximum
damping occurs when the electrical and mechanical time-scales are the same, but
the frequency shift is greatest when the resonator moves much more slowly than
the island charge. We then derive reduced master equations which describe just
the resonator dynamics. By making slightly different approximations, we obtain
two different reduced master equations for the resonator. Apart from minor
differences, the two reduced master equations give rise to a consistent picture
of the resonator dynamics which matches that obtained from the master equation
including the SET island charge.Comment: 22 pages, 4 figure
Clinical course of physiotherapy treatment response in patients with chronic low back pain- a prospective cohort study with survival analysis
Trabalho apresentado 10th Congress of European Pain Federation (EFIC), 6-9 setembro de 2017, Copenhaga, DinamarcaN/
Qualidade biológica do solo após adição de pó de balão e cultivo do milho: I - População e atividade de microrganismos.
O pó de balão ou charcok, resíduo da indústria siderúrgica não integrada a carvão vegetal enquadrado na Classe I e considerado perigoso, tem sido recomendado na cultura de eucalipto, na dosagem de 50 t ha-1. Nesse trabalho, procurou-se analisar os impactos da aplicação deste resíduo sobre a qualidade do solo cultivado com milho, medidos através da densidade populacional de fungos, bactérias e actinomicetos e hidrólise do diacetato de fluoresceína (FDA). Foram avaliados seis tratamentos constituídos de doses de pó de balão equivalentes a 0, 25, 50, 75, 100 t ha-1, na presença de adubação e de 50 t ha-1 de pó de balão, na ausência de adubação, distribuídos em delineamento de blocos casualizados, em três repetições. As amostras de solo foram coletadas após a colheita das plantas de milho, efetuada aos 60 dias de idade. Os resultados obtidos demonstraram que não houve diferença significativa na composição qualitativa e quantitativa e atividade dos microrganismos, independente das dosagens de pó de balão utilizadas. Concluiu-se que a aplicação de pó de balão não afetou a qualidade biológica do solo através dos bioindicadores utilizados, mesmo na dosagem 100 t ha-1, equivalente ao dobro da recomendada
Aharonov-Bohm ring with fluctuating flux
We consider a non-interacting system of electrons on a clean one-channel
Aharonov-Bohm ring which is threaded by a fluctuating magnetic flux. The flux
derives from a Caldeira-Leggett bath of harmonic oscillators. We address the
influence of the bath on the following properties: one- and two-particle
Green's functions, dephasing, persistent current and visibility of the
Aharonov-Bohm effect in cotunneling transport through the ring. For the bath
spectra considered here (including Nyquist noise of an external coil), we find
no dephasing in the linear transport regime at zero temperature.
PACS numbers: 73.23.-b, 73.23.Hk, 73.23.Ra, 03.65.YzComment: 17 pages, 8 figures. To be published in PRB. New version contains
minor corrections and additional discussion suggested by referee. A simple
introduction to the basics of dephasing can be found at
http://iff.physik.unibas.ch/~florian/dephasing/dephasing.htm
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