arXiv subjects

Nir Shvalb

Publications and source records attributed to Nir Shvalb.

9 recordsLinked to original sources

arXiv2025

Hypo-paradoxical Linkages: Linkages That Should Move-But Don't

While paradoxical linkages famously violate the Chebyshev-Grubler-Kutzbach criterion by exhibiting unexpected mobility, we identify an opposing phenomenon: a class of linkages that appear mobile according to the same criterion, yet are in fact rigid. We refer to these as hypo-paradoxical linkages, and proceed to analyze and illustrate their behavior. We use the same tools to further explain the unexpected positive mobility of Bennet mechanism.

physics.soc-ph↗

arXiv2024

Ramsey Approach to Quantum Mechanics

Ramsey theory enables re-shaping of the basic ideas of quantum mechanics. Quantum observables represented by linear Hermitian operators are seen as the vertices of a graph. Relations of commutation define the coloring of edges linking the vertices: if the operators commute, they are connected with a red link; if they do not commute, they are connected with a green link. Thus, a bi-colored complete Ramsey graph emerges. According to Ramsey's theorem, a complete bi-colored graph built of six vertices will inevitably contain at least one monochromatic triangle; in other words, the Ramsey number $ R(3,3) = 6 $. In our interpretation, this triangle represents the triad of observables that could or could not be established simultaneously in a given quantum system. The Ramsey approach to quantum mechanics is illustrated.

math-ph↗

arXiv2023

Navigation Through Endoluminal Channels Using Q-Learning

In this paper, we present a novel approach to navigating endoluminal channels, specifically within the bronchial tubes, using Q-learning, a reinforcement learning algorithm. The proposed method involves training a Q-learning agent to navigate a simulated environment resembling bronchial tubes, with the ultimate goal of enabling the navigation of real bronchial tubes. We discuss the formulation of the problem, the simulation environment, the Q-learning algorithm, and the results of our experiments. Our results demonstrate the agent's ability to learn effective navigation strategies and reach predetermined goals within the simulated environment. This research contributes to the development of autonomous robotic systems for medical applications, particularly in challenging anatomical environments.

cs.RO↗

arXiv2022

Ramsey Theory and Geometry of Closed Loops

We apply the Ramsey theory to the analysis of geometrical properties of closed contours. Consider a set of six points placed on a closed contour. The straight lines connecting these points are y_ik (x)=α_ik x+\b{eta}_ik (i,k=1...6), α_ik is not equal to 0. We color the edges connecting the points for which α_ik>0 holds with red, and the edges for which α_ik<0 with green with red. At least one monochromic triangle should necessarily appear within the curve (according to the Ramsey number R(3,3)=6). This result is immediately applicable for the analysis of dynamical billiards. The second theorem emerges from the combination of the Jordan curve and Ramsey theorem. The closed curve is considered. We connect the points located within the same region with green links and the points placed within the different regions with red links. In this case, transitivity/intransitivity of the relations between the points should be considered. Ramsey constructions arising from the differential geometry of closed contours are discussed.

math.DS↗

arXiv2022

Symmetric Configuration spaces of linkages

A $configuration$ of a linkage $Γ$ is a possible positioning of $Γ$ in $\mathbb{R}^d$ and the collection of all such forms the configuration space $\mathcal{C}(Γ)$ of $Γ$. We here introduce the notion of the $symmetric configuration space$ of a linkage, in which we identify configurations which are geometrically indistinguishable. We show that the symmetric configuration space of a planar polygon has a regular cell structure, provide some principles for calculating this structure, and give a complete description of the symmetric configuration space of all quadrilaterals and of the equilateral pentagon.

math.AT↗

arXiv2021

Thermophoretic Levitation of Solid Particles at Atmospheric Pressure

Separation and transportation of small particles are important processes in various applications such as the food and pharmaceutical industries. Although mechanical, chemical or electrical methods can provide possible solutions, operational or environmental constraints may require alternative methods. Spreading and levitation of clusters (aggregates) of fumed silica nanoparticles placed under atmospheric pressure on a hot plate is reported. In a closed chamber, the particles started to spread horizontally at the threshold temperature of $T_c^*=403 \pm 1$K. The powder spreading in the chamber continued until the temperature-dependent saturation value $r_{sat} (T)$, which grew linearly with the temperature. Open space experiments clearly demonstrated levitation of the powder clouds. The onset of levitation in the open space corresponded to the minimal threshold temperature of $T_o^*=373 \pm 1$K. Qualitative physical analysis of the observed phenomena is suggested. The effect of levitation is explained by the lifting thermo-phoretic force emerging in the Knudsen layer of air on the heater surface. The levitation of the powder under atmospheric pressure becomes possible due to the combination of low adhesion of the fluorinated fumed silica clusters built of nanoparticles to the substrate, relatively low density of the particles and clusters, and their high specific surface area. Ordering of the aggregates of nanoparticles within the levitating powder cloud was quantified with Voronoi diagrams.

cond-mat.soft↗

arXiv2017

Configuration spaces of spatial linkages: Taking Collisions Into Account

We construct a completed version C(Gamma) of the configuration space of a linkage Gamma in R^3 which takes into account the ways one link can touch another. We also describe a simplified version of C(Gamma) which is a blow-up of the space of immersions of Gamma in R^3 A number of simple detailed examples are given.

math.AT↗

arXiv2016

A Navigation Function For Uncertain Environment

This paper introduces a novel motion planning algorithm for stochastic scenarios. We extend the concept of a navigation function to such scenarios. Our main idea is to consider both the Gaussian distribution probabilities of the players' locations and disc (or star sets) geometry of the objects operating in the work space. We do so by formulating a probability density function that encloses both. We use the PDF to define a metric between the robot, the obstacles and the configuration space boundary. In order to define the navigation function we formulate a safe probability value for collision. By analytically investigating the PDF we find a convenient approximation for a safe distance in the sense of that metric. We prove that the resulting map is a navigation function and demonstrate our algorithm for various scenarios.

cs.RO↗

arXiv2011

Generic singular configurations of linkages

We study the topological and differentiable singularities of the configuration space C(Γ) of a mechanical linkage Γin d-dimensional Euclidean space, defining an inductive sufficient condition to determine when a configuration is singular. We show that this condition holds for generic singularities, provide a mechanical interpretation, and give an example of a type of mechanism for which this criterion identifies all singularities.

math.AT↗