280 research outputs found
A Kolmogorov Extension Theorem for POVMs
We prove a theorem about positive-operator-valued measures (POVMs) that is an
analog of the Kolmogorov extension theorem, a standard theorem of probability
theory. According to our theorem, if a sequence of POVMs G_n on
satisfies the consistency (or projectivity) condition then there is a POVM G on the space
of infinite sequences that has G_n as its marginal for
the first n entries of the sequence. We also describe an application in quantum
theory.Comment: 6 pages LaTeX, no figure
Relativistic state reduction dynamics
A mechanism describing state reduction dynamics in relativistic quantum field
theory is outlined. The mechanism involves nonlinear stochastic modifications
to the standard description of unitary state evolution and the introduction of
a relativistic field in which a quantized degree of freedom is associated to
each point in spacetime. The purpose of this field is to mediate in the
interaction between classical stochastic influences and conventional quantum
fields. The equations of motion are Lorentz covariant, frame independent, and
do not result in divergent behavior. It is shown that the mathematical
framework permits the specification of unambiguous local properties providing a
connection between the model and evidence of real world phenomena. The collapse
process is demonstrated for an idealized example.Comment: 20 pages, 2 figures, replacement with minor correction
Quantum open systems and turbulence
We show that the problem of non conservation of energy found in the
spontaneous localization model developed by Ghirardi, Rimini and Weber is very
similar to the inconsistency between the stochastic models for turbulence and
the Navier-Stokes equation. This sort of analogy may be useful in the
development of both areas.Comment: to appear in Physical Review
Quantum to Classical Transition from the Cosmic Background Radiation
We have revisited the Ghirardi-Rimini-Weber-Pearle (GRWP) approach for
continuous dynamical evolution of the state vector for a macroscopic object.
Our main concern is to recover the decoupling of the state vector dynamics for
the center-of-mass (CM) and internal motion, as in the GRWP model, but within
the framework of the standard cosmology. In this connection we have taken the
opposite direction of the GRWP argument, that the cosmic background radiation
(CBR) has originated from a fundamental stochastic hitting process. We assume
the CBR as a clue of the Big Bang, playing a main role in the decoupling of the
state vector dynamics of the CM and internal motion. In our model, instead of
describing a continuous spontaneous localization (CSL) of a system of massive
particles as proposed by Ghirardi, Pearle and Rimini, the It\^{o} stochastic
equation accounts for the intervention of the CBR on the system of particles.
Essentially, this approach leads to a pre-master equation for both the CBR and
particles degrees of freedom. The violation of the principle of energy
conservation characteristic of the CSL model is avoided as well as the
additional assumption on the size of the GRWP's localization width necessary to
reach the decoupling between the collective and internal motions. Moreover,
realistic estimation for the decoherence time, exhibiting an interesting
dependence on the CBR temperature, is obtained. From the formula for the
decoherence time it is possible to analyze the transition from micro to macro
dynamics in both the early hot Universe and the nowadays cold one. The entropy
of the system under decoherence is analyzed and the emergent `pointer basis' is
discussed. In spite of not having imposed a privileged basis, in our model the
position still emerges as the preferred observable as in the CSL model.Comment: 14 pages, no figure. To appear in Phys. Rev.
Curso agroecologia e cidadania: uma experiência de formação por alternância no Nordeste Paraense, Brasil.
O artigo mostra aspectos do curso Agroecologia e Cidadania, ministrado em regime de alternância, na Escola de Formação para Jovens Agricultores de Comunidades Rurais Amazônicas (ECRAMA), município de Santa Luzia do Pará, Nordeste Paraense. O curso é uma iniciativa da Rede Bragantina de Economia Solidária Artes e Sabores, em parceria com instituições públicas e organizações não governamentais. As atividades são divididas em tempo escola e tempo comunidade. O público alvo são jovens agricultores de comunidades rurais do Nordeste Paraense. Objetivando contribuir para o avanço do processo de desenvolvimento local sustentável, bem como a capacitação dos agricultores e agricultoras familiares, para que conduzam com eficiência a gestão dos agroecossistemas nos estabelecimentos familiares, bem como nos empreendimentos associativos da Rede Bragantina e na difusão de boas práticas de economia solidária nos municípios. Em 2016 foram realizados quatro módulos de tempo escola e em 2017 estão previsto 5 módulos, um a mais que em 2016. Os módulos presenciais do tempo escola adotam estratégias pedagógicas variadas, incluindo círculo de cultura, construção de trajetórias e relatos de experiências. As atividades do tempo comunidade complementam os conteúdos teóricos, incorporando elementos da realidade vivenciada pelos treinandos em seus estabelecimentos, comunidades e territórios.Edição dos anais do VI Congresso Latino-Americano (CLAA), X Congresso Brasileiro (CBA), V Seminário do DF e Entorno (SEMDF), 12-15 setembro de 2017, a Brasília, DF, Brasil
Quantum measurement in a family of hidden-variable theories
The measurement process for hidden-configuration formulations of quantum
mechanics is analysed. It is shown how a satisfactory description of quantum
measurement can be given in this framework. The unified treatment of
hidden-configuration theories, including Bohmian mechanics and Nelson's
stochastic mechanics, helps in understanding the true reasons why the problem
of quantum measurement can succesfully be solved within such theories.Comment: 16 pages, LaTeX; all special macros are included in the file; a
figure is there, but it is processed by LaTe
The effect of spontaneous collapses on neutrino oscillations
We compute the effect of collapse models on neutrino oscillations. The effect
of the collapse is to modify the evolution of the `spatial' part of the wave
function, which indirectly amounts to a change on the flavor components. In
many respects, this phenomenon is similar to neutrino propagation through
matter. For the analysis we use the mass proportional CSL model, and perform
the calculation to second order perturbation theory. As we will show, the CSL
prediction is very small - mainly due to the very small mass of neutrinos - and
practically undetectable.Comment: 24 pages, RevTeX. Updated versio
[Assessment of pulmonary function in a follow-up of premature infants: our experience].
Respiratory diseases are a major cause of morbidity in neonates, especially preterm infants; a long term complication of prematurity such as bronchopulmonary dysplasia (BPD) is particularly relevant today. The exact role of the Pulmonary Function Test (PFT) in this area is not yet well defined; the PFT in newborns and infants - in contrast to what happens in uncooperative children and adults - are routinely used only in a few centers. The assessment of pulmonary function in newborns and infants, however, is nowadays possible with the same reliability that in cooperative patients with the possibility to extend the assessment of polmonary function from bench to bed. The assessment of pulmonary function must be carried out with non invasive and safe methods, at the bedside, with the possibility of continuous monitoring and providing adequate calculation and management of data. The ability to assess lung function helps to define the mechanisms of respiratory failure, improving the treatment and its effects and is therefore a useful tool in the follow-up of newborn and infant with pulmonary disease
Manejo de biomassa para produção de alimentos orgânicos sem uso do fogo.
No ano de 2016 a Escola de Formação para Jovens Agricultores de Comunidades Rurais Amazônicas - ECRAMA através do projeto Homens e Mulheres, protagonistas da educação e desenvolvimento local sustentável ofereceu aos jovens egressos da ECRAMA o curso de Agroecologia e Cidadania. Teve como objetivo principal o plantio do feijão sem o uso do fogo com a introdução de adubação verde e biofertilizantes como alternativas viáveis para os agricultores familiares, assim potencializando a manutenção da biodiversidade, da floresta, dos cursos d?água, sem o uso de produtos industrializados e a necessidade do uso de recursos externos como adubação química, agrotóxicos e mecanização. Após a colheita o feijão obteve-se os seguintes rendimentos: o feijão preto em uma área total de 90 m2 produziu 4Kg, o feijão manteiguinha em uma área total de 90 m2 produziu 8 kg e o feijão bidé em uma área total de 70 m2 produziu 7kg.Edição dos anais do VI Congresso Latino-Americano (CLAA), X Congresso Brasileiro (CBA), V Seminário do DF e Entorno (SEMDF), 12-15 setembro de 2017, a Brasília, DF, Brasil
Apparent wave function collapse caused by scattering
Some experimental implications of the recent progress on wave function
collapse are calculated. Exact results are derived for the center-of-mass wave
function collapse caused by random scatterings and applied to a range of
specific examples. The results show that recently proposed experiments to
measure the GRW effect are likely to fail, since the effect of naturally
occurring scatterings is of the same form as the GRW effect but generally much
stronger. The same goes for attempts to measure the collapse caused by quantum
gravity as suggested by Hawking and others. The results also indicate that
macroscopic systems tend to be found in states with (Delta-x)(Delta-p) =
hbar/sqrt(2), but microscopic systems in highly tiltedly squeezed states with
(Delta-x)(Delta-p) >> hbar.Comment: Final published version. 20 pages, Plain TeX, no figures. Online at
http://astro.berkeley.edu/~max/collapse.html (faster from the US), from
http://www.mpa-garching.mpg.de/~max/collapse.html (faster from Europe) or
from [email protected]
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