Abstract-Tying suture knots is a time-consuming task performed frequently during Minimally Invasive Surgery (MIS).Automating this task could greatly reduce total surgery time for patients. Current solutions to this problem replay manually programmed trajectories, but a more general and robust approach is to use supervised machine learning to smooth surgeongiven training trajectories and generalize from them. Since knottying generally requires a controller with internal memory to distinguish between identical inputs that require different actions at different points along a trajectory, it would be impossible to teach the system using traditional feedforward neural nets or support vector machines. Instead we exploit more powerful, recurrent neural networks (RNNs) with adaptive internal states. Results obtained using LSTM RNNs trained by the recent Evolino algorithm show that this approach can significantly increase the efficiency of suture knot tying in MIS over preprogrammed control.

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Time-dependent density-functional theory is used to calculate the energy loss of antiprotons and protons traversing metal clusters of variable size. We find that the effective energy loss per unit path length inside the cluster shows no significant cluster size effects over the wide range of projectile velocities studied. This allows us to compare the calculated stopping power with the experimental values for a solid metal target. Excellent agreement between the theoretical results and recent experimental data is found for velocities below the inner-shell excitation threshold. We thus present a nonperturbative quantum-mechanical approach to obtain the energy loss of charges in solids.

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The stopping power of antiprotons moving at low velocities through a uniform electron gas is calculated by making use of the momentum-transfer cross section. The static screening potential required is obtained from a self-consistent nonlinear screening calculation within density-functional theory. Our results indicate that the corrections beyond linear-response theory are particularly significant for negatively charged particles. We obtain, for example, a ratio of about two for the proton and antiproton stopping powers throughout the metallic density range. This work deals with the stopping of charged particles in an homogeneous electron gas at zero temperature.When the velocity of the projectile (v) is small compared with the Fermi velocity (vF) of the electrons the energy dissipation is due to the excitation of electron-hole pairs in the steady-state transport process. We treat the idealized problem of a particle moving with constant velocity through a degenerate electron gas of density no within the framework of a scattering theory approach.The nonlinear nature of the screening and therefore the role of this in the stopping power calculations is of special interest. The density-functional theory (DFT) provides an efficient and accurate method to treat the screening nonlinearities to all orders in the projectile charge Z&. The successful application of DFT to the problem of stopping power of slow positively charged particles has been demonstrated recently. ' The study of the dependence on the sign of the projectile potential is of great importance from the viewpoint of new experimental possibilities with antiparticles.Earlier theoretical calculations were restricted to high velocities of the projectile and atomistic descriptions of the target. The higher-order term (Z~) has been interpreted as a polarization effect in the stopping material. An alternative approach, for the electron gas model, is the use of higher-order response functions, whereby the induced density fluctuation is expanded systematically in powers of the ion potential. Calculations in this scheme were performed in the plasmon-pole approximation for high-velocity ion s, and using the quadratic density response function for low-velocity ions. Since the expansion techniques rapidly become unmanageable, and the degree of improvement achieved is difficult to establish, these latter methods have considered only the Z& correction to the stopping power.In the following we present an investigation of the screening and stopping power for a low-velocity antiproton. We consider the problem for various electronic densities of the system and we make a comparison with results obtained in a perturbative approach based on dielectric theory and a simple Yukawa-type model potential. We use atomic units throughout this work. First we establish the relation between the stopping power and the scattering potential. For low velocities of the projectile the energy loss per unit path length can be written as ' dE =n pvvF atr(vF ) where vF=(3tr np)' and at, is the mom...

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The aim of the paper is to investigate the bifurcation behavior of the power-factor-correction (PFC) boost converter under a conventional peak current-mode control. The converter is operated in continuous-conduction mode. The bifurcation analysis performed by computer simulations reveals interesting effects of variation of some chosen parameters on the stability of the converter. The results are illustrated by time-domain waveforms, discrete-time maps and parameter plots. An analytical investigation confirms the results obtained by computer simulations. Such an analysis allows convenient prediction of stability boundaries and facilitates the selection of parameter values to guarantee stable operation.

We have performed self-consistent calculations of the nonlinear screening of a point charge Z in a two-dimensional electron gas using a density functional theory method. We find that the screened potential for a Z = 1 charge supports a bound state even in the high density limit where one might expect perturbation theory to apply. To explain this behaviour, we prove a theorem to show that the results of linear response theory are in fact correct even though bound states exist.PACS 73.20.Hb Screening is a fundamental property of an electron gas in arbitrary dimensions. The example of two dimensions is of particular interest because of the possible realization of quasi-two-dimensional systems in a variety of contexts: semiconductor heterostructures [1], image or band-gap surface states at metal surfaces [2], electrons on the surface of liquid helium [3], and layered materials [4]. In all of these cases, the interaction of external charges with the two-dimensional electron gas (2DEG) is a problem of both fundamental and practical interest. For example, the transport of electrons in a 2DEG is often limited by charged impurity scattering and a detailed knowledge of the scattering potential is needed for an accurate determination of the electron mobility [1]. Scanning tunnelling microscopy offers an even more direct means of determining the screening response of a quasi-2DEG through the observation of adsorbate-induced Friedel oscillations [5]. Still another class of problems involves the interaction with moving charges as might arise in low-energy electron scattering [6] or tunnelling experiments [7]. In this case, the dynamic response of the 2DEG is important in that electronic excitation, and hence energy loss, will occur.A charged impurity or projectile typically represents a strong perturbation and a nonlinear screening theory is in general needed to account for the modifications of the local electronic structure. However, in certain situations the screened impurity potential may be relatively weak and therefore amenable to a perturbative treatment. This is usually the method adopted to deal with donor impurities that are spatially removed from the 2DEG within a heterostructure [1], although it is rare to find quantitative agreement between theory and experimentally measured mobilities [8]. The situation of acceptor impurities within the gas is a much more severe perturbation and quite dramatic effects can arise as a result of the modified electronic structure [9,10]. In such situations, the screening response has to be determined nonlinearly.One of our objectives in this Letter is to provide a fully self-consistent description of the nonlinear screening in an ideal 2DEG within the context of density functional theory. A second objective is to use these calculations to establish the range of validity of linear response theory. Somewhat surprisingly, this latter objective is more subtle than anticipated as a result of a peculiarity of potential scattering in 2D, namely the fact that any purely attractive potent...