Autonomous take-off and landing of a tethered aircraft: a simulation study

The problem of autonomous launch and landing of a tethered rigid aircraft for airborne wind energy generation is addressed. The system operates with ground-based power conversion and pumping cycles, where the tether is repeatedly reeled in and out of a winch installed on the ground and linked to an electric motor/generator. In order to accelerate the aircraft to take-off speed, the ground station is augmented with a linear motion system composed by a slide translating on rails and controlled by a second motor. An onboard propeller is used to sustain the forward velocity during the ascend of the aircraft. During landing, a slight tension on the line is kept, while the onboard control surfaces are used to align the aircraft with the rails and to land again on them. A model-based, decentralized control approach is proposed, capable to carry out a full cycle of launch, low-tension flight, and landing again on the rails. The derived controller is tested via numerical simulations with a realistic dynamical model of the system, in presence of different wind speeds and turbulence, and its performance in terms of landing accuracy is assessed. This study is part of a project aimed to experimentally verify the launch and landing approach on a small-scale prototype.Comment: This is the longer version of a paper submitted to the 2016 American Control Conference 2016, with more details on the simulation parameter

Next-to-leading power threshold logarithms: a status report

There is ample evidence, dating as far back as Low's theorem, that the universality of soft emissions extends beyond leading power in the soft energy. This universality can, in principle, be exploited to generalise the formalism of threshold resummations beyond leading power in the threshold variable. In the past years, several phenomenological approaches have been partially successful in performing such a resummation. Here, we briefly review some recent developments which pave the way to a solution of this problem, at least for electroweak annihilation processes.Comment: Contribution to the Proceedings of the 12th International Symposium on Radiative Corrections (Radcor 2015) and LoopFest XIV, UCLA, 15-19 June, 201

Interpretable Model Summaries Using the Wasserstein Distance

Statistical models often include thousands of parameters. However, large models decrease the investigator's ability to interpret and communicate the estimated parameters. Reducing the dimensionality of the parameter space in the estimation phase is a commonly used approach, but less work has focused on selecting subsets of the parameters for interpreting the estimated model -- especially in settings such as Bayesian inference and model averaging. Importantly, many models do not have straightforward interpretations and create another layer of obfuscation. To solve this gap, we introduce a new method that uses the Wasserstein distance to identify a low-dimensional interpretable model projection. After the estimation of complex models, users can budget how many parameters they wish to interpret and the proposed generates a simplified model of the desired dimension minimizing the distance to the full model. We provide simulation results to illustrate the method and apply it to cancer datasets

Non-analytic behavior of the Loschmidt echo in XXZ spin chains: Exact results

We address the computation of the Loschmidt echo in interacting integrable spin chains after a quantum quench. We focus on the massless regime of the XXZ spin-1/2 chain and present exact results for the dynamical free energy (Loschmidt echo per site) for a special class of integrable initial states. For the first time we are able to observe and describe points of non-analyticities using exact methods, by following the Loschmidt echo up to large real times. The dynamical free energy is computed as the leading eigenvalue of an appropriate Quantum Transfer Matrix, and the non-analyticities arise from the level crossings of this matrix. Our exact results are expressed in terms of \u201cexcited-state\u201d thermodynamic Bethe ansatz equations, whose solutions involve non-trivial Riemann surfaces. By evaluating our formulas, we provide explicit numerical results for the quench from the N\ue9el state, and we determine the first few non-analytic points. \ua9 2018 The Author(s

Case Histories Paper: Jackup Rig Spud Can Penetration: A 6,000 Ton Load Test

One of the most exciting geotechnical problems for the offshore engineer is the prediction of mobile jack-up rig spud can penetration. Jack-up drilling rigs are used to drill offshore oil and gas wells in water depths up to about 100 m. The rigs are supported by circular “spud can” foundations fitted at the end of extendable platform legs. Upon arrival to the site the jack-up extends the legs to the sea floor and self-elevates out of the water. This action forces the spud cans into the seabed until soil capacity is attained. Prior to jacking the rig out of the water, a geotechnical borehole is made from the rig to verify soil conditions and estimate bearing capacity and leg penetration. The geotechnical engineer makes predictions of foundation capacity in real time; the predictions are then verified by the actual behavior of the footing under the 6,000 ton preload. This paper presents experience with bearing capacity predictions versus field measurements from over 15 offshore sites. Relatively simple closed form bearing capacity formulas are shown to provide good predictions for real behavior of these large scale foundations

Integrable Digital Quantum Simulation: Generalized Gibbs Ensembles and Trotter Transitions

The Trotter-Suzuki decomposition is a promising avenue for digital quantum simulation (DQS), approximating continuous-time dynamics by discrete Trotter steps of duration $\tau$. Recent work suggested that DQS is typically characterized by a sharp Trotter transition: when $\tau$ is increased beyond a threshold value, approximation errors become uncontrolled at large times due to the onset of quantum chaos. Here we contrast this picture with the case of integrable DQS. We focus on a simple quench from a spin-wave state in the prototypical XXZ Heisenberg spin chain, and study its integrable Trotterized evolution as a function of $\tau$. Due to its exact local conservation laws, the system does not heat up to infinite temperature and the late-time properties of the dynamics are captured by a discrete Generalized Gibbs Ensemble (dGGE). By means of exact calculations we find that, for small $\tau$, the dGGE depends analytically on the Trotter step, implying that discretization errors remain bounded even at infinite times. Conversely, the dGGE changes abruptly at a threshold value $\tau_{\rm th}$, signaling a novel type of Trotter transition. We show that the latter can be detected locally, as it is associated with the appearance of a non-zero staggered magnetization with a subtle dependence on $\tau$. We highlight the differences between continuous and discrete GGEs, suggesting the latter as novel interesting nonequilibrium states exclusive to digital platforms.Comment: 6+13 pages, 3+4 figure

Your Paper has been Accepted, Rejected, or Whatever: Automatic Generation of Scientific Paper Reviews

4noPeer review is widely viewed as an essential step for ensuring scientific quality of a work and is a cornerstone of scholarly publishing. On the other hand, the actors involved in the publishing process are often driven by incentives which may, and increasingly do, undermine the quality of published work, especially in the presence of unethical conduits. In this work we investigate the feasibility of a tool capable of generating fake reviews for a given scientific paper automatically. While a tool of this kind cannot possibly deceive any rigorous editorial procedure, it could nevertheless find a role in several questionable scenarios and magnify the scale of scholarly frauds. A key feature of our tool is that it is built upon a small knowledge base, which is very important in our context due to the difficulty of finding large amounts of scientific reviews. We experimentally assessed our method 16 human subjects. We presented to these subjects a mix of genuine and machine generated reviews and we measured the ability of our proposal to actually deceive subjects judgment. The results highlight the ability of our method to produce reviews that often look credible and may subvert the decision.partially_openembargoed_20160915Bartoli, Alberto; De Lorenzo, Andrea; Medvet, Eric; Tarlao, FabianoBartoli, Alberto; DE LORENZO, Andrea; Medvet, Eric; Tarlao, Fabian