Quantum noise in ideal operational amplifiers

We consider a model of quantum measurement built on an ideal operational amplifier operating in the limit of infinite gain, infinite input impedance and null output impedance and with a feddback loop. We evaluate the intensity and voltage noises which have to be added to the classical amplification equations in order to fulfill the requirements of quantum mechanics. We give a description of this measurement device as a quantum network scattering quantum fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe

Back-action cancellation in interferometers by quantum locking

We show that back-action noise in interferometric measurements such as gravitational-waves detectors can be completely suppressed by a local control of mirrors motion. An optomechanical sensor with an optimized measurement strategy is used to monitor mirror displacements. A feedback loop then eliminates radiation-pressure effects without adding noise. This very efficient technique leads to an increased sensitivity for the interferometric measurement, which becomes only limited by phase noise. Back-action cancellation is furthermore insensitive to losses in the interferometer.Comment: 4 pages, 3 figures, RevTe

DNA uptake into nuclei: Numerical and analytical results

The dynamics of polymer translocation through a pore has been the subject of recent theoretical and experimental works. We have considered theoretical estimates and performed computer simulations to understand the mechanism of DNA uptake into the cell nucleus, a phenomenon experimentally investigated by attaching a small bead to the free end of the double helix and pulling this bead with the help of an optical trap. The experiments show that the uptake is monotonous and slows down when the remaining DNA segment becomes very short. Numerical and analytical studies of the entropic repulsion between the DNA filament and the membrane wall suggest a new interpretation of the experimental observations. Our results indicate that the repulsion monotonically decreases as the uptake progresses. Thus, the DNA is pulled in (i) either by a small force of unknown origin, and then the slowing down can be interpreted only statistically; (ii) or by a strong but slow ratchet mechanism, which would naturally explain the observed monotonicity, but then the slowing down requires additional explanations. Only further experiments can unambiguously distinguish between these two mechanisms.Comment: 12 pages, 6 figures, submitted to J. Phys. Cond. Ma

Inhibition of in-stent stenosis by oral administration of bindarit in porcine coronary arteries

<p><b>Objective:</b> We have previously demonstrated that bindarit, a selective inhibitor of monocyte chemotactic proteins (MCPs), is effective in reducing neointimal formation in rodent models of vascular injury by reducing smooth muscle cell proliferation and migration and neointimal macrophage content, effects associated with the inhibition of MCP-1/CCL2 production. The aim of the current study was to evaluate the efficacy of bindarit on in-stent stenosis in the preclinical porcine coronary stent model.</p> <p><b>Methods and Results:</b> One or 2 bare metal stents (Multi-Link Vision, 3.5 mm) were deployed (1:1.2 oversize ratio) in the coronary arteries of 42 pigs (20 bindarit versus 22 controls). Bindarit (50 mg/kg per day) was administered orally from 2 days before stenting until the time of euthanasia at 7 and 28 days. Bindarit caused a significant reduction in neointimal area (39.4%, P<0.001, n=9 group), neointimal thickness (51%, P<0.001), stenosis area (37%, P<0.001), and inflammatory score (40%, P<0.001) compared with control animals, whereas there was no significant difference in the injury score between the 2 groups. Moreover, treatment with bindarit significantly reduced the number of proliferating cells (by 45%, P<0.05; n=6 group) and monocyte/macrophage content (by 55%, P<0.01; n=5–6 group) in stented arteries at day 7 and 28, respectively. These effects were associated with a significant (P<0.05) reduction of MCP-1 plasma levels at day 28. In vitro data showed that bindarit (10–300 micromol/L) reduced tumor necrosis factor-alpha (50 ng/mL)–induced pig coronary artery smooth muscle cell proliferation and inhibited MCP-1 production.</p> <p><b>Conclusion:</b> Our results show the efficacy of bindarit in the prevention of porcine in-stent stenosis and support further investigation for clinical application of this compound.</p&gt

Foam front propagation in anisotropic oil reservoirs

The pressure-driven growth model is considered, describing the motion of a foam front through an oil reservoir during foam improved oil recovery, foam being formed as gas advances into an initially liquid-filled reservoir. In the model, the foam front is represented by a set of so called ‘material points’ that track the advance of gas into the liquid-filled region. According to the model, the shape of the foam front is prone to develop concave sharply-curved concavities, where the orientation of the front changes rapidly over a small spatial distance: these are referred to as 'concave corners'. These concave corners need to be propagated differently from the material points on the foam front itself. Typically the corner must move faster than those material points, otherwise spurious numerical artifacts develop in the comp uted shape of the front. A propagation rule or ‘speed up’ rule is derived for the concave corners, which is shown to be sensitive to the level of anisotropy in the permeability of the reservoir and also sensitive to the orientation of the corners themselves. In particular if a corner in an anisotropic reservoir were to be propagated according to an isotropic speed up rule, this might not be sufficient to suppress spurious numerical artifacts, at least for certain orientations of the corner. On the other hand, systems that are both heterogeneous and anisotropic tend to be well behaved numerically, regard less of whether one uses the isotropic or anisotropic speed up rule for corners. This comes about be cause, in the heterogeneous and anisotropic case, the orientation of the corner is such that the 'correct' anisotropic speed is just very slightly less than the ‘incorrect’ isotropic one. The anisotropic rule does however manage to keep the corner very slightly sharper than the isotropic rule does

Quantum fluctuations for drag free geodesic motion

The drag free technique is used to force a proof mass to follow a geodesic motion. The mass is protected from perturbations by a cage, and the motion of the latter is actively controlled to follow the motion of the proof mass. We present a theoretical analysis of the effects of quantum fluctuations for this technique. We show that a perfect drag free operation is in principle possible at the quantum level, in spite of the back action exerted on the mass by the position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change