4,444 research outputs found
Controlling chaos in the quantum regime using adaptive measurements
The continuous monitoring of a quantum system strongly influences the
emergence of chaotic dynamics near the transition from the quantum regime to
the classical regime. Here we present a feedback control scheme that uses
adaptive measurement techniques to control the degree of chaos in the
driven-damped quantum Duffing oscillator. This control relies purely on the
measurement backaction on the system, making it a uniquely quantum control, and
is only possible due to the sensitivity of chaos to measurement. We quantify
the effectiveness of our control by numerically computing the quantum Lyapunov
exponent over a wide range of parameters. We demonstrate that adaptive
measurement techniques can control the onset of chaos in the system, pushing
the quantum-classical boundary further into the quantum regime
Quantum field effects in coupled atomic and molecular Bose-Einstein condensates
This paper examines the parameter regimes in which coupled atomic and
molecular Bose-Einstein condensates do not obey the Gross-Pitaevskii equation.
Stochastic field equations for coupled atomic and molecular condensates are
derived using the functional positive-P representation. These equations
describe the full quantum state of the coupled condensates and include the
commonly used Gross-Pitaevskii equation as the noiseless limit. The model
includes all interactions between the particles, background gas losses,
two-body losses and the numerical simulations are performed in three
dimensions. It is found that it is possible to differentiate the quantum and
semiclassical behaviour when the particle density is sufficiently low and the
coupling is sufficiently strong.Comment: 4 postscript figure
Collapsing Bose-Einstein condensates beyond the Gross-Pitaevskii approximation
We analyse quantum field models of the bosenova experiment, in which
Rb Bose-Einstein condensates were made to collapse by switching their
atomic interactions from repulsive to attractive. Specifically, we couple the
lowest order quantum field correlation functions to the Gross-Pitaevskii
function, and solve the resulting dynamical system numerically. Comparing the
computed collapse times with the experimental measurements, we find that the
calculated times are much larger than the measured values. The addition of
quantum field corrections does not noticeably improve the agreement compared to
a pure Gross-Pitaevskii theory.Comment: 8 pages, 4 figure
Lay support for pregnant women with social risk: a randomised controlled trial
OBJECTIVES We sought evidence of effectiveness of lay support to improve maternal and child outcomes in disadvantaged families. DESIGN Prospective, pragmatic individually randomised controlled trial. SETTING Three Maternity Trusts in West Midlands, UK. PARTICIPANTS Following routine midwife systematic assessment of social risk factors 1324 nulliparous women were assigned, using telephone randomisation, to standard maternity care or addition of referral to a Pregnancy Outreach Worker (POW) service. Under 16 years and teenagers recruited to the Family Nurse Partnership trial were excluded. INTERVENTIONS Pregnancy Outreach Workers were trained to provide individual support and case management for the women including home visiting from randomisation to six weeks after birth. Standard maternity care (control) included provision for referring women with social risk factors to specialist midwifery services, available to both arms. MAIN OUTCOME MEASURES Primary outcomes were antenatal visits attended and Edinburgh Postnatal Depression Scale (EPDS) 8–12 weeks postpartum. Pre–specified, powered subgroup comparison was among women with two or more social risks. Secondary outcomes included maternal and neonatal birth outcomes; maternal self-efficacy and mother-to-infant bonding at 8-12 weeks; child development assessment at six weeks, breastfeeding at six weeks and immunisation uptake at 4 months, all collected from routine child health systems. RESULTS Antenatal attendances were high in the standard care control and did not increase further with addition of the POW intervention (10·1 versus 10·1 (MD) –0·00, 95% CI, (95% CI, –0·37, 0·37)). In the powered sub-group of women with two or more social risk factors, mean EPDS (MD –0·79 (95% CI, –1·56, –0·02) was significantly better, although for all women recruited no significant differences were seen (mean difference (MD) –0·59 (95% CI, –1·24, 0·06)). Mother-to-infant bonding was significantly better in the intervention group for all women (MD-0.30 (95% CI, -0.61, -0.00) p=0.05) and there were no differences in other secondary outcomes. CONCLUSIONS This trial demonstrates differences in depressive symptomatology with addition of the POW service in the powered sub-group of women with two or more social risk factors. Addition to existing evidence indicates benefit from lay interventions in preventing postnatal depression. This finding is important for women and their families given the known effect of maternal depression on longer term childhood outcomes
Effects of Dietary Antioxidant Supplementation on Cattle Finished with 30% Wet Distillers Grains Plus Solubles on Fatty Acid Profiles and Display Life
Steers were finished on either 0% wet distillers grains plus solubles or 30% wet distillers grains plus solubles with four antioxidant treatments to evaluate the effects of finishing diets containing wet distillers grains plus solubles, vitamin E and Agrado Plus on beef fatty acid profiles, discoloration and lipid oxidation of retail- displayed beef. Th e inclusion of 30% wet distillers grains plus solubles increased total polyunsaturated fatty acids of beef, but did not promote discoloration or lipid oxidation compared to the 0% wet distillers grains plus solubles diet. In both diets, feeding vitamin E alone or vitamin E+ Agrado Plus was effective in reducing lipid oxidation and maintaining color stability, while supplementing Agrado Plus alone had minimal effects in improving lipid and color stability
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