Globally Guided Trajectory Planning in Dynamic Environments

Navigating mobile robots through environments shared with humans is challenging. From the perspective of the robot, humans are dynamic obstacles that must be avoided. These obstacles make the collision-free space nonconvex, which leads to two distinct passing behaviors per obstacle (passing left or right). For local planners, such as receding-horizon trajectory optimization, each behavior presents a local optimum in which the planner can get stuck. This may result in slow or unsafe motion even when a better plan exists. In this work, we identify trajectories for multiple locally optimal driving behaviors, by considering their topology. This identification is made consistent over successive iterations by propagating the topology information. The most suitable high-level trajectory guides a local optimization-based planner, resulting in fast and safe motion plans. We validate the proposed planner on a mobile robot in simulation and real-world experiments.Comment: 7 pages, 6 figures, accepted to IEEE International Conference on Robotics and Automation (ICRA) 202

Homography-based ground plane detection using a single on-board camera

This study presents a robust method for ground plane detection in vision-based systems with a non-stationary camera. The proposed method is based on the reliable estimation of the homography between ground planes in successive images. This homography is computed using a feature matching approach, which in contrast to classical approaches to on-board motion estimation does not require explicit ego-motion calculation. As opposed to it, a novel homography calculation method based on a linear estimation framework is presented. This framework provides predictions of the ground plane transformation matrix that are dynamically updated with new measurements. The method is specially suited for challenging environments, in particular traffic scenarios, in which the information is scarce and the homography computed from the images is usually inaccurate or erroneous. The proposed estimation framework is able to remove erroneous measurements and to correct those that are inaccurate, hence producing a reliable homography estimate at each instant. It is based on the evaluation of the difference between the predicted and the observed transformations, measured according to the spectral norm of the associated matrix of differences. Moreover, an example is provided on how to use the information extracted from ground plane estimation to achieve object detection and tracking. The method has been successfully demonstrated for the detection of moving vehicles in traffic environments

Factorizing numbers with classical interference: several implementations in optics

Truncated Fourier, Gauss, Kummer and exponential sums can be used to factorize numbers: for a factor these sums equal unity in absolute value, whereas they nearly vanish for any other number. We show how this factorization algorithm can emerge from superpositions of classical light waves and we present a number of simple implementations in optics

Simple proof of gauge invariance for the S-matrix element of strong-field photoionization

The relationship between the length gauge (LG) and the velocity gauge (VG) exact forms of the photoionization probability amplitude is considered. Our motivation for this paper comes from applications of the Keldysh-Faisal-Reiss (KFR) theory, which describes atoms (or ions) in a strong laser field (in the nonrelativistic approach, in the dipole approximation). On the faith of a certain widely-accepted assumption, we present a simple proof that the well-known LG form of the exact photoionization (or photodetachment) probability amplitude is indeed the gauge-invariant result. In contrast, to obtain the VG form of this probability amplitude, one has to either (i) neglect the well-known Goeppert-Mayer exponential factor (which assures gauge invariance) during all the time evolution of the ionized electron or (ii) put some conditions on the vector potential of the laser field.Comment: The paper was initially submitted (in a previous version) on 16 October 2006 to J. Phys. A and rejected. This is the extended version (with 2 figures), which is identical to the paper published online on 12 December 2007 in Physica Script

Laparoscopy for management of nontraumatic acute abdomen

Secţia Chirurgie, Spitalul Municipal de Urgenţă, Moineşti, România, Al XII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova cu participare internațională 23-25 septembrie 2015Introducere: Laparoscopia în abdomenul acut are atât rol în stabilirea diagnosticului, confirmându-l în situaţiile echivoce, cât şi în orientarea strategiei terapeutice cu avantajele chirurgiei mini-invazive. Material şi metode: Studiul nostru evaluează 873 de cazuri de abdomen acut nontraumatic (exceptând colecistita acută) abordate laparoscopic în perioada 2010-2014, urmarindu-se concordanţa diagnosticului pre- şi postoperator, stabilirea unui diagnostic intraoperator cert, incidenţa intervenţiilor laparoscopice cât şi complicaţiile acestora. Rezultate: Diagnosticul intraoperator a fost de apendicită acută în 653 (75%) de cazuri, urgenţele ginecologice au fost certificate la 146 (17%) de pacienţi (chist ovarian eclatat, sarcina extrauterină, boala inflamatorie pelvină), 52 (6%) de pacienţi au fost diagnosticaţi cu ulcer perforat, 22 de cazuri fiind înregistrate cu alte patologii (pancreatite acute, perforaţii intestinale cu peritonite, diverticul Meckel perforat, infarcte enteromezenterice, peritonita TBC). Incidente şi accidente au fost întâlnite la 56 (6,5%) de pacienţi, au fost înregistrate 33 (3,7%) de conversii, complicaţii postoperatorii fiind înregistrate în 37 (4,2%) de cazuri. Concluzii: Laparoscopia diagnostică este o modalitate optimă diagnostică în cazurile de abdomen acut non-traumatic, fiind salutară în cazurile de apendicită acută, urgenţe ginecologice şi peritonita de etiologie neprecizată cu posibilitatea rezolvării pe această cale a patologiei identificate, în abdomenul acut laparoscopia fiind ultimul mijloc diagnostic şi primul mijloc terapeutic.Aims: Laparoscopy for acute abdomen is important either for diagnostic, when there is uncertainty in establishing the etiology, and also has a therapeutic role with the well known advantages of mini-invasive surgery. Material and methods: Our study evaluates 873 patients of nontraumatic acute abdomen (excepting acute cholecystitis), approached laparoscopically during 2010-2014. The following factors were pursued: the concordance between pre- and postoperative diagnostic, the establishment of a certain intraoperative diagnostic, incidence of laparoscopic interventions and their complications. Results: There were 653 (75%) cases of acute appendicitis, 146 patients with gynecological (ruptured ovarian cyst, ectopic pregnancy, inflammatory pelvic disease), 52 (6%) patients with perforated ulcer, 22 cases with other pathologies (acute pancreatitis, enteral perforations, perforations of Meckel diverticulum, entero-mesenteric infarction, tuberculous peritonitis), confirmed laparoscopically. Incidents and accidents were encountered in 56 (6.5%) cases, there were 33 (3.7%) conversions to open technique and for 37 (4.2%) patients were recorded postoperative complications. Conclusions: Diagnostic laparoscopy is an optimal method of diagnostic confirmation for cases of non-traumatic acute abdomen especially for acute appendicitis, gynecological emergencies and peritonitis of unknown etiology with the possibility of laparoscopic treatment of these pathologies, being also the last option for diagnostic and the first solution for treatment

Decay versus survival of a localized state subjected to harmonic forcing: exact results

We investigate the survival probability of a localized 1-d quantum particle subjected to a time dependent potential of the form $rU(x)\sin{\omega t}$ with $U(x)=2\delta (x-a)$ or $U(x)= 2\delta(x-a)-2\delta (x+a)$. The particle is initially in a bound state produced by the binding potential $-2\delta (x)$. We prove that this probability goes to zero as $t\to\infty$ for almost all values of $r$, $\omega$, and $a$. The decay is initially exponential followed by a $t^{-3}$ law if $\omega$ is not close to resonances and $r$ is small; otherwise the exponential disappears and Fermi's golden rule fails. For exceptional sets of parameters $r,\omega$ and $a$ the survival probability never decays to zero, corresponding to the Floquet operator having a bound state. We show similar behavior even in the absence of a binding potential: permitting a free particle to be trapped by harmonically oscillating delta function potential