A comparative study of smear layer removal and erosion in apical intraradicular dentine with three irrigating solutions: a scanning electron microscopy evaluation

Introduction: This study compared the efficacy of BioPure MTAD (Dentsply Tulsa, Tulsa, OK), 17% EDTA, and 42% citric acid in endodontic smear layer removal and degree of erosion in the apical third of endodontic canals. Methods: Ninety-six extracted single-rooted human teeth were randomized into four groups (n = 24) and instrumented using System GT nickel-titanium rotary instruments (Dentsply Tulsa, Tulsa, OK). Each canal was irrigated with one of the following solutions: BioPure MTAD, 17% EDTA, 42% citric acid, or 5.25% NaOCl (control). Next, all specimens were irrigated with 5.25% NaOCl. Results: Evaluation by scanning electron microscopy showed no significant differences among test irrigants in removing the smear layer. However, the efficacy of BioPure MTAD and 17% EDTA in removing the smear layer was significantly greater than 5.25% NaOCl (control). The erosive effects of irrigating solutions could not be evaluated. Conclusions: In conclusion, the protocols used in this study were not sufficient to completely remove the smear layer in the apical third of prepared root canals. © 2009 American Association of Endodontists

Nonlinear control of leader-follower formation flying

This paper considers the problem of relative motion control involved in a leader-follower formation keeping mission. More specifically, center of mass dynamics of two Earth orbiting satellite is modeled, including the nonlinearity due to Earth oblateness. Next, the differential algebra is exploited to compute an high order Taylor expansion of the State-Dependent Riccati Equation (SDRE) solution. This new approach reduces the computational cost of the online Algebraic Riccati Equation solution required by SDRE algorithm; in fact, the differential algebraic formulation gives a polynomial representation which can be directly evaluated for SDRE solutions or exploited to define an initial first guess for iterative SDRE algorithms

Diffraction limited optics for single atom manipulation

We present an optical system designed to capture and observe a single neutral atom in an optical dipole trap, created by focussing a laser beam using a large numerical aperture N.A.=0.5 aspheric lens. We experimentally evaluate the performance of the optical system and show that it is diffraction limited over a broad spectral range (~ 200 nm) with a large transverse field (+/- 25 microns). The optical tweezer created at the focal point of the lens is able to trap single atoms of 87Rb and to detect them individually with a large collection efficiency. We measure the oscillation frequency of the atom in the dipole trap, and use this value as an independent determination of the waist of the optical tweezer. Finally, we produce with the same lens two dipole traps separated by 2.2 microns and show that the imaging system can resolve the two atoms.Comment: 8 pages, 9 figures; typos corrected and references adde

Propagation of Large Uncertainty Sets in Orbital Dynamics by Automatic Domain Splitting

Current approaches to uncertainty propagation in astrodynamics mainly refer to linearized models or Monte Carlo simulations. Naive linear methods fail in nonlinear dynamics, whereas Monte Carlo simulations tend to be computationally intensive. Differential algebra has already proven to be an efficient compromise by replacing thousands of pointwise integrations of Monte Carlo runs with the fast evaluation of the arbitrary order Taylor expansion of the flow of the dynamics. However, the current implementation of the DA-based high-order uncertainty propagator fails when the non-linearities of the dynamics prohibit good convergence of the Taylor expansion in one or more directions. We solve this issue by introducing automatic domain splitting. During propagation, the polynomial expansion of the current state is split into two polynomials whenever its truncation error reaches a predefined threshold. The resulting set of polynomials accurately tracks uncertainties, even in highly nonlinear dynamics. The method is tested on the propagation of (99942) Apophis post-encounter motion

An automatic domain splitting technique to propagate uncertainties in highly nonlinear orbital dynamics

Current approaches to uncertainty propagation in astrodynamics mainly refer to linearized models or Monte Carlo simulations. Naive linear methods fail in nonlinear dynamics, whereas Monte Carlo simulations tend to be computationally intensive. Differential algebra has already proven to be an efficient compromise by replacing thousands of pointwise integrations of Monte Carlo runs with the fast evaluation of the arbitrary order Taylor expansion of the flow of the dynamics. However, the current implementation of the DA-based high-order uncertainty propagator fails in highly nonlinear dynamics or long term propagation. We solve this issue by introducing automatic domain splitting. During propagation, the polynomial of the current state is split in two polynomials when its accuracy reaches a given threshold. The resulting polynomials accurately track uncertainties, even in highly nonlinear dynamics. The method is tested on the propagation of (99942) Apophis post-encounter motion

Smear layer removal and canal cleanliness using different irrigation systems (EndoActivator, EndoVac, and Passive Ultrasonic Irrigation) : Field Emission Scanning Electron Microscopic Evaluation in an In Vitro Study.

Abstract Introduction: The purpose of this study was to evaluate the effectiveness of different irrigating methods in removing the smear layer at 1, 3, 5, and 8 mm from the apex of endodontic canals. Methods: Sixty-five extracted single-rooted human mandibular premolars were decoronated to a standardized length of 16 mm. Specimens were shaped to ProTaper F4 (Dentsply Maillefer, Ballaigues, Switzerland) and irrigated with 5.25% NaOCl at 37 C. Teeth were divided into 5 groups (2 control groups [n = 10] and 3 test groups [n = 15]) according to the final irrigant activation/delivering technique (ie, sonic irrigation, passive ultrasonic irrigation [PUI], or apical negative pressure). Root canals were then split longitudinally and observed by field emission scanning electron microscopy. The presence of debris and a smear layer at 1, 3, 5, and 8 mm from the apex was evaluated. Scores were analyzed by Kruskal- Wallis and Mann-Whitney U tests. Results: The EndoActivator System (Dentsply Tulsa Dental Specialties, Tulsa, OK) was significantly more efficient than PUI and the control groups in removing the smear layer at 3, 5, and 8 mm from the apex. The EndoVac System (Discus Dental, Culver City, CA) removed statistically significantly more smear layer than all groups at 1, 3, 5, and 8 mm from the apex. At 5 and 8 mm from the apex, PUI and the EndoVac did not differ statistically significantly, but both performed statistically better than the control groups. Conclusions: In our study, none of the activation/delivery systems completely removed the smear layer from the endodontic dentine walls; nevertheless, the EndoActivator and EndoVac showed the best results at 3, 5, and 8 mm (EndoActivator) and 1, 3, 5, and 8 mm (EndoVac) from the apex. (J Endod 2013;39:1456–1460

Characterisation of Mega-Constellation Links for LEO Missions with Applications to EO and ISS Use Cases

Satellite missions demand ever greater connectivity, especially in the LEO regime. In this paper, we introduce the new mega-constellation services in space paradigm: we show that mega constellations, deployed to offer innovative services to Earth’s users, can provide excellent connectivity to LEO spacecrafts, too. First, we characterise the communication link between space users and the actual OneWeb and Starlink constellations. A full set of results in terms of availability, access duration, Doppler, and path losses as a function of user orbital parameters, identifying optimal user orbits, is provided. The results achieved by a multi-system user able to communicate with both fleets are also presented. The potential improvements available if geostationary constellations are used to complement LEO mega constellations in a multi-orbit system are discussed, too. Finally, we focus on two LEO use cases, the International Space Station and an Earth Observation Sun Synchronous satellite. All the results demonstrate the numerous advantages of the mega-constellation connectivity solution, which is able to transform LEO spacecrafts into highly responsive nodes of a space-to-space networ

Hybrid Differential Dynamic Programming Algorithm for Low-Thrust Trajectory Design Using Exact High-Order Transition Maps

Optimal orbital trajectories are obtained through the solution of highly nonlinear large-scale problems. In the case of low-thrust propulsion applications, the spacecraft benefits from high specific impulses and, hence, greater payload mass. However, these missions require a high count of orbital revolutions and, therefore, display augmented sensitivity to many disturbances. Solutions to such problems can be tackled via a discrete approach, using optimal feedback control laws. Historically, differential dynamic programming (DDP) has shown outstanding results in tackling these problems. A state of the art software that implements a variation of DDP has been developed by Whiffen (2006) and it is used by NASA’s DAWN mission. One of the latest techniques implemented to deal with these discrete constrained optimizations is the Hybrid Differential Dynamic Programming (HDDP) algorithm, introduced by Lantoine and Russell (2012). This method complements the reliability and efficiency of classic nonlinear programming techniques with the robustness to poor initial guesses and the reduced computational effort of DDP. The key feature of the algorithm is the exploitation of a second order state transition matrix procedure to propagate the needed partials, decoupling the dynamics from the optimization. In doing so, it renders the integration of dynamical equations suitable for parallelization. Together with the possibility to treat constrained problems, this represents the greatest improvement of classic DDP. Nevertheless, the major limitation of this approach is the high computational cost to evaluate the required state transition matrices. Analytical derivatives, when available, have shown a significant reduction in the computational cost and time for HDDP application. This work applies differential algebra (DA) to HDDP to cope with this limitation. DA is introduced to obtain state transition matrices as polynomial maps. These maps come directly from the integration of the dynamics of the system, removing the dedicated algorithmic step and reducing its computational cost. Moreover, by operating on polynomial maps, all the solutions of local optimization problems are treated through differential algebraic techniques. This approach allows users to deal with higher order expansions of the cost, without modifying the algorithm. From the examples provided, it emerges that increasing the order of the expansions does not yield a better convergence rate. Additionally, it causes numerical instability of the algorithm to arise, as well as a noticeable increase on computational time due to the number of polynomial coefficients that ought to be computed