Quantum-limited directional amplifiers with optomechanics

Directional amplifiers are an important resource in quantum information processing, as they protect sensitive quantum systems from excess noise. Here, we propose an implementation of phase-preserving and phase-sensitive directional amplifiers for microwave signals in an electromechanical setup comprising two microwave cavities and two mechanical resonators. We show that both can reach their respective quantum limits on added noise. In the reverse direction, they emit thermal noise stemming from the mechanical resonators and we discuss how this noise can be suppressed, a crucial aspect for technological applications. The isolation bandwidth in both is of the order of the mechanical linewidth divided by the amplitude gain. We derive the bandwidth and gain-bandwidth product for both and find that the phase-sensitive amplifier has an unlimited gain-bandwidth product. Our study represents an important step toward flexible, on-chip integrated nonreciprocal amplifiers of microwave signals

Hysteresis and bi-stability by an interplay of calcium oscillations and action potential firing

Many cell types exhibit oscillatory activity, such as repetitive action potential firing due to the Hodgkin-Huxley dynamics of ion channels in the cell membrane or reveal intracellular inositol triphosphate (IP$_3$) mediated calcium oscillations (CaOs) by calcium-induced calcium release channels (IP$_3$-receptor) in the membrane of the endoplasmic reticulum (ER). The dynamics of the excitable membrane and that of the IP$_3$-mediated CaOs have been the subject of many studies. However, the interaction between the excitable cell membrane and IP$_3$-mediated CaOs, which are coupled by cytosolic calcium which affects the dynamics of both, has not been studied. This study for the first time applied stability analysis to investigate the dynamic behavior of a model, which includes both an excitable membrane and an intracellular IP$_3$-mediated calcium oscillator. Taking the IP$_3$ concentration as a control parameter, the model exhibits a novel rich spectrum of stable and unstable states with hysteresis. The four stable states of the model correspond in detail to previously reported growth-state dependent states of the membrane potential of normal rat kidney fibroblasts in cell culture. The hysteresis is most pronounced for experimentally observed parameter values of the model, suggesting a functional importance of hysteresis. This study shows that the four growth-dependent cell states may not reflect the behavior of cells that have differentiated into different cell types with different properties, but simply reflect four different states of a single cell type, that is characterized by a single model.Comment: 29 pages, 6 figure

Using local and historical data to enhance understanding of spatial and temporal rainfall patterns

Farmers face uncertainty in their businesses from many factors, but rainfall is a key determinant of both the nature of the production system and variation in financial returns. Currently, various weather forecasting services are available from the Australian Bureau of Meteorology (BoM) based on about 7000 stations covering all of Australia. Seasonal Climate Forecasts are seen as another tool that can help to improve farm productivity. It is well known that many farmers keep their own rainfall records, and likely that the farmers have a high degree of confidence in their own records. Australian Bureau of Statistics figures indicate that there were possibly 7000 grain related ‘agricultural businesses’ in NSW alone in 2009/10 indicating that there is the potential to increase data density by up to an order of magnitude. This project is part of a broader study to improve rainfall predictions for grain farmers using data collected locally to the users (crowd sourcing). The data is collected directly on farm, and from other sources which may be available. The focus is on the historical data, its collection and analysis, in terms of discerning patterns in time and space which may help provide a local framework, within which coarser scale forecasts can be interpreted and understood. Data will be stored on secure database systems at the University of Sydney. Results indicate that farm data does provide more local detail, temporally and spatially. Deficit and surplus analysis demonstrates the predictive capacity of the local temporal data, despite limited data precluding the definition of ideal criteria and parameters for predictive ‘similar year’ selection. The spatial data demonstrates quantifiable site specific differences from institutional data. Testing across more climate types may allow these differences to be defined within and across regions. Tests for an indicator time period show that farm rainfall in the early part of the growing season (April and May) may indeed be indicative of seasonal condtions, while more data is needed to confirm this. The use of southern oscillation life cycle information to select appropriate years considerably improved the relationships revealed, with a doubling of relationship strength across all climatic types, although the strength of the relationships differed across the climatic types, and the strongest relationships were split between the months of April and May. More extensive analysis, with more data across more BoM districts (and therefore climate classes) will be required to confirm this conclusion, but it appears that farm rainfall records and SOI information can provide an indicator time period to help farmers interpret, refine and utilise seasonal forecasts

Dynamical Landau-de Gennes Theory for Electrically-Responsive Liquid Crystal Networks

Liquid crystal networks combine the orientational order of liquid crystals with the elastic properties of polymer networks, leading to a vast application potential in the field of responsive coatings, e.g., for haptic feedback, self-cleaning surfaces and static and dynamic pattern formation. Recent experimental work has further paved the way toward such applications by realizing the fast and reversible surface modulation of a liquid crystal network coating upon in-plane actuation with an AC electric field. Here, we construct a Landau-type theory for electrically-responsive liquid crystal networks and perform Molecular Dynamics simulations to explain the findings of these experiments and inform on rational design strategies. Qualitatively, the theory agrees with our simulations and reproduces the salient experimental features. We also provide a set of testable predictions: the aspect ratio of the nematogens, their initial orientational order when cross-linked into the polymer network and the cross-linking fraction of the network all increase the plasticization time required for the film to macroscopically deform. We demonstrate that the dynamic response to oscillating electric fields is characterized by two resonances, which can likewise be influenced by varying these parameters, providing an experimental handle to fine-tune device design

A globally efficient means of distributing UTC time and frequency through GPS

Time and frequency outputs comparable in quality to the best laboratories have been demonstrated on an integrated system suitable for field application on a global basis. The system measures the time difference between 1 pulse-per-second (pps) signals derived from local primary frequency standards and from a multi-channel GPS C/A receiver. The measured data is processed through optimal SA Filter algorithms that enhance both the stability and accuracy of GPS timing signals. Experiments were run simultaneously at four different sites. Even with large distances between sites, the overall results show a high degree of cross-correlation of the SA noise. With sufficiently long simultaneous measurement sequences, the data shows that determination of the difference in local frequency from an accepted remote standard to better than 1 x 10(exp -14) is possible. This method yields frequency accuracy, stability, and timing stability comparable to that obtained with more conventional common-view experiments. In addition, this approach provides UTC(USNO MC) in real time to an accuracy better than 20 ns without the problems normally associated with conventional common-view techniques. An experimental tracking loop was also set up to demonstrate the use of enhanced GPS for dissemination of UTC(USNO MC) over a wide geographic area. Properly disciplining a cesium standard with a multi-channel GPS receiver, with additional input from USNO, has been found to permit maintaining a timing precision of better than 10 ns between Palo Alto, CA and Washington, DC

Double Exchange Alone Does Not Explain the Resistivity of La1−xSrxMnO3La_{1-x} Sr_x MnO_3

The $La_{1-x} Sr_x MnO_3$ system with $0.2 \lesssim x \lesssim 0.4$ has traditionally been modelled with a ``double exchange'' Hamiltonian, in which it is assumed that the only relevant physics is the tendency of carrier hopping to line up neighboring spins. We present a solution of the double exchange model, show it is incompatible with many aspects of the resistivity data, and propose that a strong electron-phonon interaction arising from a Jahn-Teller splitting of the outer Mn d-level plays a crucial role.Comment: Figure available via concentional mail. Contact [email protected]

Expression profiling of immune inhibitory Siglecs and their ligands in patients with glioma

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