Optical read out and feedback cooling of a nanostring optomechanical cavity

Optical measurement of the motion of a 940 kHz mechanical resonance of a silicon nitride nanostring resonator is demonstrated with a read out noise imprecision reaching 37 dB below that of the resonator's zero-point fluctuations. Via intensity modulation of the optical probe laser, radiation pressure feedback is used to cool and damp the mechanical mode from an initial room temperature occupancy of $\bar{n}_{b} = 6.5 \times 10^6$ ($T_{b}=295$K) down to a phonon occupation of $\langle n \rangle = 66 \pm 10$, representing a mode temperature of $T_{m} \approx 3$mK. The five decades of cooling is enabled by the system's large single-photon cooperativity $(C_{1} = 4)$ and high quantum efficiency of optical motion detection ($\eta_{t} = 0.27$).Comment: 13 pages, 13 figure

Large-Amplitude, Pair-Creating Oscillations in Pulsar and Black Hole Magnetospheres

A time-dependent model for pair creation in a pulsar magnetosphere is developed. It is argued that the parallel electric field that develops in a charge-starved region (a gap) of a pulsar magnetosphere oscillates with large amplitude. Electrons and positrons are accelerated periodically and the amplitude of the oscillations is assumed large enough to cause creation of upgoing and downgoing pairs at different phases of the oscillation. With a charge-starved initial condition, we find that the oscillations result in bursts of pair creation in which the pair density rises exponentially with time. The pair density saturates at $N_\pm\simeq E_{0}^2/(8\pi m_ec^2\Gamma_{\rm thr})$, where $E_0$ is the parallel electric field in the charge-starved initial state, and $\Gamma_{\rm thr}$ is the Lorentz factor for effec tive pair creation. The frequency of oscillations following the pair creation burst is given roughly by $\omega_{\rm osc}=eE_0/(8m_ec\Gamma_{\rm thr})$. A positive feedback keeps the system stable, such that the average pair creation rate balances the loss rate due to pairs escaping the magnetosphere.Comment: 21 pages, 6 figures, ApJ submitte

Observation of Quantum Motion of a Nanomechanical Resonator

In this Letter we use resolved sideband laser cooling to cool a mesoscopic mechanical resonator to near its quantum ground state (phonon occupancy 2.6±0.2), and observe the motional sidebands generated on a second probe laser. Asymmetry in the sideband amplitudes provides a direct measure of the displacement noise power associated with quantum zero-point fluctuations of the nanomechanical resonator, and allows for an intrinsic calibration of the phonon occupation number

Nonlinear radiation pressure dynamics in an optomechanical crystal

Utilizing a silicon nanobeam optomechanical crystal, we investigate the attractor diagram arising from the radiation pressure interaction between a localized optical cavity at $\lambda = 1552$nm and a mechanical resonance at $\omega/2\pi = 3.72$GHz. At a temperature of $T \approx 10$K, highly nonlinear driving of mechanical motion is observed via continuous wave optical pumping. Introduction of a time-dependent (modulated) optical pump is used to steer the system towards an otherwise inaccessible dynamically stable attractor in which mechanical self-oscillation occurs for an optical pump red-detuned from the cavity resonance. An analytical model incorporating thermo-optic effects due to optical absorption heating is developed, and found to accurately predict the measured device behavior.Comment: 5 pages, 3 figure

Suppression of inflammation by helminths: a role for the gut microbiota?

Multiple recent investigations have highlighted the promise of helminth-based therapies for the treatment of inflammatory disorders of the intestinal tract of humans, including inflammatory bowel disease and coeliac disease. However, the mechanisms by which helminths regulate immune responses, leading to the amelioration of symptoms of chronic inflammation are unknown. Given the pivotal roles of the intestinal microbiota in the pathogenesis of these disorders, it has been hypothesized that helminth-induced modifications of the gut commensal flora may be responsible for the therapeutic properties of gastrointestinal parasites. In this article, we review recent progress in the elucidation of host-parasite-microbiota interactions in both animal models of chronic inflammation and humans, and provide a working hypothesis of the role of the gut microbiota in helminth-induced suppression of inflammation.Funding from the Isaac Newton Trust / Wellcome Trust ISSF / University of Cambridge Joint Research Grants Scheme (C.C.) and the Australian National Health and Medical Research Council (NHMRC) grants 1037304, 1020114 (A.L.), 1052938 (C.C.) and 613718 (P.G.) is gratefully acknowledged.This is the final version of the article. It first appeared from Royal Society Publishing via http://dx.doi.org/10.1098/rstb.2014.029

Nitrogen/palladium-codoped TiO² for efficient visible light photocatalytic dye degradation

Please refer to full text to view abstrac