70 research outputs found
Cavity quantum electro-optics. II. Input-output relations between traveling optical and microwave fields
In the previous paper [M. Tsang, Phys. Rev. A 81, 063837 (2010), e-print
arXiv:1003.0116], I proposed a quantum model of a cavity electro-optic
modulator, which can coherently couple an optical cavity mode to a microwave
resonator mode and enable novel quantum operations on the two modes, including
laser cooling of the microwave mode, electro-optic entanglement, and
backaction-evading optical measurement of a microwave quadrature. In this
sequel, I focus on the quantum input-output relations between traveling optical
and microwave fields coupled to a cavity electro-optic modulator. With
red-sideband optical pumping, the relations are shown to resemble those of a
beam splitter for the traveling fields, so that in the ideal case of zero
parasitic loss and critical coupling, microwave photons can be coherently
up-converted to "flying" optical photons with unit efficiency, and vice versa.
With blue-sideband pumping, the modulator acts as a nondegenerate parametric
amplifier, which can generate two-mode squeezing and hybrid entangled photon
pairs at optical and microwave frequencies. These fundamental operations
provide a potential bridge between circuit quantum electrodynamics and quantum
optics.Comment: 12 pages, 10 figures, v2: updated and submitte
Excess Body Weight and Gait Influence Energy Cost of Walking in Older Adults
Purpose: To study how excess body weight influences the energy cost of walking (Cw) and determine if overweight and obese older adults self-select stride frequency to minimize Cw.
Methods: Using body mass index (BMI) men and women between the ages of 65–80 yr were separated into normal weight (NW, BMI ≤ 24.9 kg m−2, n = 13) and overweight-obese groups (OWOB, BMI ≥25.0 kg m−2, n = 13). Subjects walked at 0.83 m s−1 on an instrumented treadmill that recorded gait parameters, and completed three, six-minute walking trials; at preferred stride frequency (PSF), at +10% PSF, and at −10% PSF. Cw was determined by indirect calorimetry. Repeated measures analysis of variance was used to compare groups, and associations were tested with Pearson correlations, α = 0.05.
Results: OWOB had 62% greater absolute Cw (301 ± 108 vs. 186 ± 104 J m−1, P \u3c 0.001) and 20% greater relative Cwkg (3.48 ± 0.95 vs. 2.91 ± 0.94 J kg−1 m−1, P = 0.046) than NW. Although PSF was not different between OWOB and NW (P = 0.626), Cw was 8% greater in OWOB at +10% PSF (P \u3c 0.001). At PSF OWOB spent less time in single-limb support (33.1 ± 1.5 vs. 34.9 ± 1.6 %GC, P = 0.021) and more time in double-limb support (17.5 ± 1.6 vs. 15.4 ± 1.4 %GC, P = 0.026) than NW. In OWOB, at PSF, Cw was correlated to impulse (r = −0.57, P = 0.027) and stride frequency (r = 0.51, P = 0.046).
Conclusions: Excess body weight is associated with greater Cw in older adults, possibly contributing to reduced mobility in overweight and obese older persons
The value of nonlinear control theory in investigating the underlying dynamics and resilience of a grocery supply chain
In an empirical context, a method to use nonlinear control theory in the dynamic analysis of supply chain resilience is developed and tested. The method utilises block diagram development, transfer function formulation, describing function representation of nonlinearities and simulation. Using both ‘shock’ or step response and ‘filter’ or frequency response lenses, a system dynamics model is created to analyse the resilience performance of a distribution centre replenishment system at a large grocery retailer. Potential risks for the retailer’s resilience performance include the possibility of a mismatch between supply and demand, as well as serving the store inefficiently and causing on-shelf stock-outs. Thus, resilience is determined by investigating the dynamic behaviour of stock and shipment responses. The method allows insights into the nonlinear system control structures that would not be evident using simulation alone, including a better understanding of the influence of control parameters on dynamic behaviour, the identification of inventory offsets potentially leading to ‘drift’, the impact of nonlinearities on supply chain performance and the minimisation of simulation experiments
Frequency Domain Analysis Reveals External Periodic Fluctuations Can Generate Sustained p53 Oscillation
p53 is a well-known tumor suppressor protein that regulates many pathways, such as ones involved in cell cycle and apoptosis. The p53 levels are known to oscillate without damping after DNA damage, which has been a focus of many recent studies. A negative feedback loop involving p53 and MDM2 has been reported to be responsible for this oscillatory behavior, but questions remain as how the dynamics of this loop alter in order to initiate and maintain the sustained or undamped p53 oscillation. Our frequency domain analysis suggests that the sustained p53 oscillation is not completely dictated by the negative feedback loop; instead, it is likely to be also modulated by periodic DNA repair-related fluctuations that are triggered by DNA damage. According to our analysis, the p53-MDM2 feedback mechanism exhibits adaptability in different cellular contexts. It normally filters noise and fluctuations exerted on p53, but upon DNA damage, it stops performing the filtering function so that DNA repair-related oscillatory signals can modulate the p53 oscillation. Furthermore, it is shown that the p53-MDM2 feedback loop increases its damping ratio allowing p53 to oscillate at a frequency more synchronized with the other cellular efforts to repair the damaged DNA, while suppressing its inherent oscillation-generating capability. Our analysis suggests that the overexpression of MDM2, observed in many types of cancer, can disrupt the operation of this adaptive mechanism by making it less responsive to the modulating signals after DNA damage occurs
A preliminary investigation into the design of pressure cushions and their potential applications for forearm robotic orthoses
Virtual-Design-Model-Based Pressure-Tracking Control of High-Dynamic Pneumatic Valves Using a Sliding Mode Controller Combined with a Proportional-Integral-Derivative Scheme
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