43,563 research outputs found
Plane waves in noncommutative fluids
We study the dynamics of the noncommutative fuid in the Snyder space
perturbatively at the first order in powers of the noncommutative parameter.
The linearized noncommutative fluid dynamics is described by a system of
coupled linear partial differential equations in which the variables are the
fluid density and the fluid potentials. We show that these equations admit a
set of solutions that are monocromatic plane waves for the fluid density and
two of the potentials and a linear function for the third potential. The
energy-momentum tensor of the plane waves is calculated.Comment: 11 pages. Version published as a Lette
Integrability of a disordered Heisenberg spin-1/2 chain
We investigate how the transition from integrability to nonintegrability
occurs by changing the parameters of the Hamiltonian of a Heisenberg spin-1/2
chain with defects. Randomly distributed defects may lead to quantum chaos. A
similar behavior is obtained in the presence of a single defect out of the
edges of the chain, suggesting that randomness is not the cause of chaos in
these systems, but the mere presence of a defect.Comment: 4 pages, 4 figure
Interaction-free measurements by quantum Zeno stabilisation of ultracold atoms
Quantum mechanics predicts that our physical reality is influenced by events
that can potentially happen but factually do not occur. Interaction-free
measurements (IFMs) exploit this counterintuitive influence to detect the
presence of an object without requiring any interaction with it. Here we
propose and realize an IFM concept based on an unstable many-particle system.
In our experiments, we employ an ultracold gas in an unstable spin
configuration which can undergo a rapid decay. The object - realized by a laser
beam - prevents this decay due to the indirect quantum Zeno effect and thus,
its presence can be detected without interacting with a single atom. Contrary
to existing proposals, our IFM does not require single-particle sources and is
only weakly affected by losses and decoherence. We demonstrate confidence
levels of 90%, well beyond previous optical experiments.Comment: manuscript with 5 figures, 3 supplementary figure, 1 supplementary
not
0.75 atoms improve the clock signal of 10,000 atoms
Since the pioneering work of Ramsey, atom interferometers are employed for
precision metrology, in particular to measure time and to realize the second.
In a classical interferometer, an ensemble of atoms is prepared in one of the
two input states, whereas the second one is left empty. In this case, the
vacuum noise restricts the precision of the interferometer to the standard
quantum limit (SQL). Here, we propose and experimentally demonstrate a novel
clock configuration that surpasses the SQL by squeezing the vacuum in the empty
input state. We create a squeezed vacuum state containing an average of 0.75
atoms to improve the clock sensitivity of 10,000 atoms by 2.05 dB. The SQL
poses a significant limitation for today's microwave fountain clocks, which
serve as the main time reference. We evaluate the major technical limitations
and challenges for devising a next generation of fountain clocks based on
atomic squeezed vacuum.Comment: 9 pages, 6 figure
Análise da produção de fitohormônios por Gluconacetobacter diazotrophicus influenciada pelas condições de operação de um bioreator em batelada.
Laser Cooling of Trapped Fermi Gases deeply below the Fermi Temperature
We study the collective Raman cooling of a polarized trapped Fermi gas in the
Festina Lente regime, when the heating effects associated with photon
reabsorptions are suppressed. We predict that by adjusting the spontaneous
Raman emission rates and using appropriately designed anharmonic traps,
temperatures of the order of 2.7% of the Fermi temperature can be achieved in
3D.Comment: 4 pages, 3 figures; final versio
Aplicação de ácido húmico via fertirrigação na produtividade da bananeira BRS Tropical.
Os ácidos húmicos constituem a maior fração da matéria orgânica do solo. A parte mais estável do carbono presente na matéria orgânica do solo e são cruciais no conceito de desenvolvimento sustentável, devido à sua influência na manutenção da qualidade do solo
The Association between Different Levels of Alcohol Use and Gait under Single and Dual Task in Community-Dwelling Older Persons Aged 65 to 70 Years.
Objectives. This study aimed to describe the cross-sectional and longitudinal association between alcohol intake and gait parameters in older persons. Methods. Community-dwelling persons aged 65-70 years (N = 807). Information on health, functional status, and alcohol use was self-reported at baseline and at 3-year follow-up, whereas gait speed and stride-to-stride variability were measured while walking only (single task) and under dual tasking (counting backwards). Results. Compared to light-to-moderate drinking, heavy drinking was associated with slower gait speed in single task (adj. coeff.: -.040, 95% CI: -.0.78 to -.002, p = .035). No significant association was observed between heavy drinking and gait speed variability. Nondrinkers walked significantly slower than light-to-moderate drinkers in dual task and had significantly higher gait speed variability in both single and dual task, but these associations disappeared after adjustment for comorbidity. At follow-up, 35.2% and 34.1% of the participants walked significantly slower in single and dual task, respectively. This proportion varied a little across drinking categories. Conclusion. At baseline, heavy alcohol consumption was significantly associated with slower gait speed in single task. Selective survival of the fittest heavy drinkers probably explains why this association faded in longitudinal analyses. The trend of poorer gait performance in nondrinkers disappeared after adjustment for comorbidity, suggesting confounding by a worse health status
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