Extreme stresses can be produced in nanoscale structures; this feature has been used to realize enhanced materials properties, such as the high mobility of silicon in modern transistors. We show how ...nanoscale stress can be used to realize exceptionally low mechanical dissipation when combined with "soft-clamping"-a form of phononic engineering. Specifically, using a nonuniform phononic crystal pattern, we colocalize the strain and flexural motion of a free-standing silicon nitride nanobeam. Ringdown measurements at room temperature reveal string-like vibrational modes with quality (
) factors as high as 800 million and
× frequency exceeding 10
hertz. These results illustrate a promising route for engineering ultracoherent nanomechanical devices.
In real-time quantum feedback protocols, the record of a continuous measurement is used to stabilize a desired quantum state. Recent years have seen successful applications of these protocols in a ...variety of well-isolated micro-systems, including microwave photons and superconducting qubits. However, stabilizing the quantum state of a tangibly massive object, such as a mechanical oscillator, remains very challenging: the main obstacle is environmental decoherence, which places stringent requirements on the timescale in which the state must be measured. Here we describe a position sensor that is capable of resolving the zero-point motion of a solid-state, 4.3-megahertz nanomechanical oscillator in the timescale of its thermal decoherence, a basic requirement for real-time (Markovian) quantum feedback control tasks, such as ground-state preparation. The sensor is based on evanescent optomechanical coupling to a high-Q microcavity, and achieves an imprecision four orders of magnitude below that at the standard quantum limit for a weak continuous position measurement--a 100-fold improvement over previous reports--while maintaining an imprecision-back-action product that is within a factor of five of the Heisenberg uncertainty limit. As a demonstration of its utility, we use the measurement as an error signal with which to feedback cool the oscillator. Using radiation pressure as an actuator, the oscillator is cold damped with high efficiency: from a cryogenic-bath temperature of 4.4 kelvin to an effective value of 1.1 ± 0.1 millikelvin, corresponding to a mean phonon number of 5.3 ± 0.6 (that is, a ground-state probability of 16 per cent). Our results set a new benchmark for the performance of a linear position sensor, and signal the emergence of mechanical oscillators as practical subjects for measurement-based quantum control.
Super Bomb Ken Young, Warner R. Schilling
2020, 2020-02-15
eBook
Super Bomb unveils the story of the events leading up to President Harry S. Truman's 1950 decision to develop a "super, " or hydrogen, bomb. That fateful decision and its immediate consequences are ...detailed in a diverse and complete account built on newly released archives and previously hidden contemporaneous interviews with more than sixty political, military, and scientific figures who were involved in the decision. Ken Young and Warner R. Schilling present the expectations, hopes, and fears of the key individuals who lobbied for and against developing the H-bomb. They portray the conflicts that arose over the H-bomb as rooted in the distinct interests of the Atomic Energy Commission, the Los Alamos laboratory, the Pentagon and State Department, the Congress, and the White House. But as they clearly show, once Truman made his decision in 1950, resistance to the H-bomb opportunistically shifted to new debates about the development of tactical nuclear weapons, continental air defense, and other aspects of nuclear weapons policy. What Super Bomb reveals is that in many ways the H-bomb struggle was a proxy battle over the morality and effectiveness of strategic bombardment and the role and doctrine of the US Strategic Air Command.
Abstract Context Transcatheter ablation of atrial fibrillation (AF) has undergone important development, with acceptable midterm results in terms of the safety and recurrence. A meta-analysis was ...performed to identify the periprocedural complications, midterm success rates and predictors of recurrence after AF ablation. Methods and results 4357 patients with paroxysmal AF, 1083 with persistent AF and 1777 with long standing AF were included. The pooled analysis showed that there was an in-hospital complication rate of tamponade requiring drainage of 0.99% (0.44–1.54; CI 99%), stroke with neurological persistent impairment of 0.22% (0.04–0.47; CI 99%), and stroke without of 0.36% (0.03–0.70; CI 99%) After a follow up of 22 (13–28) months and 1.23 (1.19–1.5; CI 99%) procedures per patient, the AF recurrence rate was 31.20% (24.87–34.81; CI 99%). The persistent AF patients exhibited a greater risk of recurrence after the first ablation (OR 1.78 1.14, 2.77 CI 99%), but a trend towards non significance was present in the patients with more than one procedure (OR 1.69 0.95, 3.00 CI 99%). The most powerful predictors of an AF ablation failure in the overall population were a recurrence within 30-days (OR 4.30; 2.00–10.80), valvular AF (OR 5.20; 2.22–9.50) and a left atrium diameter of more than 50 mm (OR 5.10 2.00–12.90; all CI 95%). Conclusions Persistent AF remains burdened from higher recurrence rates, however not so following redo-procedures. Three predictors, valvular AF, a left atrium diameter longer than 50 mm and recurrence within 30 days, could be appraised to drive selection of patients and therapeutic strategy.
When an optical field is reflected from a compliant mirror, its intensity and phase become quantum-correlated due to radiation pressure. These correlations form a valuable resource: the mirror may be ...viewed as an effective Kerr medium generating squeezed states of light, or the correlations may be used to erase backaction from an interferometric measurement of the mirror’s position. To date, optomechanical quantum correlations have been observed in only a handful of cryogenic experiments, owing to the challenge of distilling them from thermomechanical noise. Accessing them at room temperature, however, would significantly extend their practical impact, with applications ranging from gravitational wave detection to chip-scale accelerometry. Here, we observe broadband quantum correlations developed in an optical field due to its interaction with a room-temperature nanomechanical oscillator, taking advantage of its high-cooperativity near-field coupling to an optical microcavity. The correlations manifest as a reduction in the fluctuations of a rotated quadrature of the field, in a frequency window spanning more than an octave below mechanical resonance. This is due to coherent cancellation of the two sources of quantum noise contaminating the measured quadrature—backaction and imprecision. Supplanting the backaction force with an off-resonant test force, we demonstrate the working principle behind a quantum-enhanced “variational” force measurement.
Acquired or intrinsic resistance to apoptotic and necroptotic stimuli is considered a major hindrance of therapeutic success in malignant melanoma. Inhibitor of apoptosis proteins (IAPs) are ...important regulators of apoptotic and necroptotic cell death mediated by numerous cell death signalling platforms. In this report we investigated the impact of IAPs for cell death regulation in malignant melanoma. Suppression of IAPs strongly sensitized a panel of melanoma cells to death ligand-induced cell death, which, surprisingly, was largely mediated by apoptosis, as it was completely rescued by addition of caspase inhibitors. Interestingly, the absence of necroptosis signalling correlated with a lack of receptor-interacting protein kinase-3 (RIPK3) mRNA and protein expression in all cell lines, whereas primary melanocytes and cultured nevus cells strongly expressed RIPK3. Reconstitution of RIPK3, but not a RIPK3-kinase dead mutant in a set of melanoma cell lines overcame CD95L/IAP antagonist-induced necroptosis resistance independent of autocrine tumour necrosis factor secretion. Using specific inhibitors, functional studies revealed that RIPK3-mediated mixed-lineage kinase domain-like protein (MLKL) phosphorylation and necroptosis induction critically required receptor-interacting protein kinase-1 signalling. Furthermore, the inhibitor of mutant BRAF Dabrafenib, but not Vemurafenib, inhibited necroptosis in melanoma cells whenever RIPK3 is present. Our data suggest that loss of RIPK3 in melanoma and selective inhibition of the RIPK3/MLKL axis by BRAF inhibitor Dabrafenib, but not Vemurafenib, is critical to protect from necroptosis. Strategies that allow RIPK3 expression may allow unmasking the necroptotic signalling machinery in melanoma and points to reactivation of this pathway as a treatment option for metastatic melanoma.
Quantum correlations between imprecision and backaction are a hallmark of continuous linear measurements. Here, we study how measurement-based feedback can be used to improve the visibility of ...quantum correlations due to the interaction of a laser field with a nanomechanical oscillator. Backaction imparted by the meter laser, due to radiation-pressure quantum fluctuations, gives rise to correlations between its phase and amplitude quadratures. These quantum correlations are observed in the experiment both as squeezing of the meter field fluctuations below the vacuum level in a homodyne measurement and as sideband asymmetry in a heterodyne measurement, demonstrating the common origin of both phenomena. We show that quantum feedback, i.e., feedback that suppresses measurement backaction, can be used to increase the visibility of the sideband asymmetry ratio. In contrast, by operating the feedback loop in the regime of noise squashing, where the in-loop photocurrent variance is reduced below the vacuum level, the visibility of the sideband asymmetry is reduced. This is due to backaction arising from vacuum noise in the homodyne detector. These experiments demonstrate the possibility, as well as the fundamental limits, of measurement-based feedback as a tool to manipulate quantum correlations.
Super Bomb Ken Young; Warner R. Schilling
01/2020
eBook
Super Bomb unveils the story of the events leading up to President Harry S. Truman's 1950 decision to develop a "super," or hydrogen, bomb. That fateful decision and its immediate consequences are ...detailed in a diverse and complete account built on newly released archives and previously hidden contemporaneous interviews with more than sixty political, military, and scientific figures who were involved in the decision.
Ken Young and Warner R. Schilling present the expectations, hopes, and fears of the key individuals who lobbied for and against developing the H-bomb. They portray the conflicts that arose over the H-bomb as rooted in the distinct interests of the Atomic Energy Commission, the Los Alamos laboratory, the Pentagon and State Department, the Congress, and the White House. But as they clearly show, once Truman made his decision in 1950, resistance to the H-bomb opportunistically shifted to new debates about the development of tactical nuclear weapons, continental air defense, and other aspects of nuclear weapons policy. WhatSuper Bomb reveals is that in many ways the H-bomb struggle was a proxy battle over the morality and effectiveness of strategic bombardment and the role and doctrine of the US Strategic Air Command.
Cardiac implantable electronic device (CIED) infection is an increasingly common complication of device therapy. CIED infection confers significant patient morbidity and health care expenditure, ...hence it is essential that clinicians recognise the contemporary strategies for predicting, reducing and treating these events. Recent technological advances—in particular, the development of antimicrobial envelopes, leadless devices and validated risk scores—present decision-makers with novel strategies for managing this expanding patient population. This review summarises the key issues facing CIED patients and their physicians, and explores the supporting evidence for the latest therapeutic developments in this field.
For late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) assessment of atrial scar to guide management and targeting of ablation in atrial fibrillation (AF), an objective, ...reproducible method of identifying atrial scar is required.
To describe an automated method for operator-independent quantification of LGE that correlates with colocated endocardial voltage and clinical outcomes.
LGE CMR imaging was performed at 2 centers, before and 3 months after pulmonary vein isolation for paroxysmal AF (n = 50). A left atrial (LA) surface scar map was constructed by using automated software, expressing intensity as multiples of standard deviation (SD) above blood pool mean. Twenty-one patients underwent endocardial voltage mapping at the time of pulmonary vein isolation (11 were redo procedures). Scar maps and voltage maps were spatially registered to the same magnetic resonance angiography (MRA) segmentation.
The LGE levels of 3, 4, and 5SDs above blood pool mean were associated with progressively lower bipolar voltages compared to the preceding enhancement level (0.85 ± 0.33, 0.50 ± 0.22, and 0.38 ± 0.28 mV; P = .002, P < .001, and P = .048, respectively). The proportion of atrial surface area classified as scar (ie, >3 SD above blood pool mean) on preablation scans was greater in patients with postablation AF recurrence than those without recurrence (6.6% ± 6.7% vs 3.5% ± 3.0%, P = .032). The LA volume >102 mL was associated with a significantly greater proportion of LA scar (6.4% ± 5.9% vs 3.4% ± 2.2%; P = .007).
LA scar quantified automatically by a simple objective method correlates with colocated endocardial voltage. Greater preablation scar is associated with LA dilatation and AF recurrence.
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