arXiv subjects

Skanda Vivek

Publications and source records attributed to Skanda Vivek.

8 recordsLinked to original sources

arXiv2021

Quantifying Urban Road Network Vulnerability and Resilience to Attacks

The rise of connected and autonomous vehicles, combined with the proliferation of IoT and connected surfaces, lead to the emergence of novel complex cyber risks. Lack of encryption and authentication in internal vehicular networks are widely recognized as cause for concern by cybersecurity experts, automobile, and OEM manufacturers. This concern has only been growing with the increase in cybersecurity incidents and demonstrations showing different vehicular vulnerabilities, making it nearly impossible to completely secure vehicles against cyber-attacks. Of particular concern is the potential for large-scale vehicular cyber-attacks to cascade to transportation networks, which are the lifeline of cities. Here, we develop a framework based on complex network theory, traffic flow, and new data based technologies to quantify the vulnerability of city-scale transportation to cyber-attacks. Application of our framework to the road network of Boston reveals that targeted attacks on a small fraction of nodes leads to disproportionately larger disruptions of routes. We develop an early-detection framework to quantify real-time risk based on gathering multidimensional traffic flow, incident, and social media data sets. Our results illustrate an effects based approach to transportation cyber-defense, through informed, intelligent vehicular agents.

physics.soc-ph↗

arXiv2019

Cyber-physical risks of hacked Internet-connected vehicles

The integration of automotive technology with Internet-connectivity promises to both dramatically improve transportation, while simultaneously introducing the potential for new unknown risks. Internet-connected vehicles are like digital data because they can be targeted for malicious hacking. Unlike digital data, however, Internet-connected vehicles are cyber-physical systems that physically interact with each other and their environment. As such, the extension of cybersecurity concerns into the cyber-physical domain introduces new possibilities for self-organized phenomena in traffic flow. Here, we study a scenario envisioned by cybersecurity experts leading to a large number of Internet-connected vehicles being suddenly and simultaneously disabled. We investigate post-hack traffic using agent-based simulations, and discover the critical relevance of percolation for probabilistically predicting the outcomes on a multi-lane road in the immediate aftermath of a vehicle-targeted cyber attack. We develop an analytic percolation-based model to rapidly assess road conditions given the density of disabled vehicles and apply it to study the street network of Manhattan (NY, USA) revealing the city's vulnerability to this particular cyber-physical attack.

cs.CR↗

arXiv2018

Collective behavior and emergent risks in a model of human- and autonomously-driven vehicles

While much effort has been invested in studies of traffic flow as a physics problem, two emerging trends in technology have broadened the subject for new investigations. The first trend is the development of self-driving vehicles. This highly-anticipated shift from human- to autonomous-drivers is expected to offer substantial benefits for traffic throughput by streamlining large-scale collective behavior. The second trend is the widespread hacking of Internet-connected devices, which as of 2015, includes vehicles. While the first proof-of-concept automobile hack was done at the single-vehicle scale, undesirable collective effects can easily arise if this activity becomes more common. Motivated by these two trends, we explore the phenomena that arise in an active matter model with lanes and lane-changing behavior. Our model incorporates a simplified minimal description of essential differences between human- and autonomous-drivers. We study the emergent collective behavior as the population of vehicles shifts from all-human to all-autonomous. Within the context of our model, we explore a worst-case scenario where Internet-connected autonomous vehicles are disabled simultaneously and \textit{en masse}. Our approach reveals a model-independent role for percolation in interpreting the results. A broad lesson our work highlights is that seemingly minor malicious activity can ultimately have major impacts when magnified through the action of collective behavior.

physics.soc-ph↗

arXiv2017

Decoupling of translational and rotational diffusion in quasi-2D colloidal fluids

We observe the translational and rotational diffusion of dimer tracer particles in quasi-2D colloidal samples. The dimers are in dense samples of two different sizes of spherical colloidal particles, with the area fraction $ϕ$ of the particles varying from dilute to nearly glassy. At low $ϕ$ rotational and translational diffusion have a ratio set by the dimer size, as expected. At higher $ϕ$ dimers become caged by their neighboring particles, and both rotational and translational diffusion slow. For short dimers we observe rapid reorientations so that the rotational diffusion is faster than translational diffusion: the two modes of diffusion are decoupled and have different $ϕ$ dependence. Longer dimers do not exhibit fast rotations, and we find translational and rotational diffusion stay coupled for all $ϕ$. Our results bridge prior results that used spheres (very fast rotation) and long ellipsoids (very slow rotation).

cond-mat.soft↗

arXiv2017

Life in the coffee-ring: how evaporation-driven density gradients dictate the outcome of inter-bacterial competition

When a drop dries, it often leaves a ring-shaped stain through a ubiquitous phenomenon known as the coffee-ring effect. This also occurs when the liquid contains suspended microbes; evaporation leaves cells at higher concentrations in the ring than the drop interior. Using biofilm experiments and cellular automata simulations, we show that the physical structure created by the coffee-ring effect can dramatically alter the outcome of inter-bacterial competition. We experimentally study this effect using two strains of $\textit{Vibrio cholerae}$ that compete using a contact-dependent killing mechanism termed the type 6 secretion system. By creating a heterogeneous density profile, the coffee-ring effect changes the outcome of competition: the bacterial strain that wins in the low-density interior loses in the far denser ring. Through simulations parameterized with experimentally-determined density profiles, we recapitulate our experimental findings. We examine the role of a $\textit{V. cholerae}$ strain's frequency, its relative efficacy at killing competitors, and the initial concentration of cells in the droplet in determining the outcome of competition. By scaling from individual cellular interactions to overall changes in strain frequency, our work demonstrates how the coffee-ring effect plays a powerful role in structuring microbial communities, indirectly driving ecological changes in community composition.

cond-mat.soft↗

arXiv2016

Long Wavelength Fluctuations and the Glass Transition in 2D and 3D

Phase transitions significantly differ between two-dimensional and three-dimensional systems, but the influence of dimensionality on the glass transition is unresolved. We use microscopy to study colloidal systems as they approach their glass transitions at high concentrations, and find differences between 2D and 3D. We find that in 2D particles can undergo large displacements without changing their position relative to their neighbors, in contrast with 3D. This is related to Mermin-Wagner long-wavelength fluctuations that influence phase transitions in 2D. However, when measuring particle motion only relative to their neighbors, 2D and 3D have similar behavior as the glass transition is approached, showing that the long wavelength fluctuations do not cause a fundamental distinction between 2D and 3D glass transitions.

cond-mat.soft↗

arXiv2014

Soap films as two-dimensional fluids: Diffusion and flow fields

We observe tracer particles diffusing in soap films to measure the two-dimensional (2D) viscous properties of the films. We make soap films with a variety of water-glycerol mixtures and of differing thicknesses. The single-particle diffusivity relates closely to parameters of the film (such as thickness $h$) for thin films, but the relation breaks down for thicker films. Notably, the diffusivity is faster than expected for thicker films, with the transition at $h/d = 5.2 \pm 0.9$ using the tracer particle diameter $d$. This indicates a transition from purely 2D diffusion to diffusion that is more three-dimensional. Additionally, we measure larger length scale flow fields from correlated particle motions and find good agreement with what is expected from theory of 2D fluids for all our films, thin and thick. We measure the effective 2D viscosity of a soap film using single-particle diffusivity measurements in thin films, and using the two-particle correlation measurements in all films.

cond-mat.soft↗

arXiv2014

Temporal and spatial heterogeneity in aging colloids: a mesoscopic model

A coarse-grained model of dense hard sphere colloids building on simple notions of particle mobility and spatial coherence is presented and shown to reproduce results of experiments and simulations for key quantities such as the intermediate scattering function, the particle mean-square displacement and the $χ_{4}$ mobility correlation function. All results are explained by two emerging and interrelated dynamical properties: i) a rate of intermittent events, quakes, which decreases as the inverse of the system age t; ii) a length scale characterizing correlated domains, which increases linearly in log t. This leads to simple and accurate scaling forms expressed in terms of a single scaling variable Finally, we propose a method to experimentally extract the growing length scale of an aging colloid and suggest that a suitable scaling of the probability density function of particle displacement can experimentally reveal the rate of quakes.

cond-mat.soft↗