Internal Avalanches in a Granular Medium

Avalanches of grain displacements can be generated by creating local voids within the interior of a granular material at rest in a bin. Modeling such a two-dimensional granular system by a collection of mono-disperse discs, the system on repeated perturbations, shows all signatures of Self-Organized Criticality. During the propagation of avalanches the competition among grains creates arches and in the critical state a distribution of arches of different sizes is obtained. Using a cellular automata model we demonstrate that the existence of arches determines the universal behaviour of the model system.Comment: 4 pages (Revtex), Four ps figures (included

Solid-fluid transition in a granular shear flow

The rheology of a granular shear flow is studied in a quasi-2d rotating cylinder. Measurements are carried out near the midpoint along the length of the surface flowing layer where the flow is steady and non-accelerating. Streakline photography and image analysis are used to obtain particle velocities and positions. Different particle sizes and rotational speeds are considered. We find a sharp transition in the apparent viscosity ($\eta$) variation with rms velocity ($u$). In the fluid-like region above the depth corresponding to the transition point (higher rms velocities) there is a rapid increase in viscosity with decreasing rms velocity. Below the transition depth we find $\eta \propto u^{-1.5}$ for all the different cases studied and the material approaches an amorphous solid-like state deep in the layer. The velocity distribution is Maxwellian above the transition point and a Poisson velocity distribution is obtained deep in the layer. The observed transition appears to be analogous to a glass transition.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let

Hands free adjustment of the microscope in microneurosurgery

A wide array of medical errors plague the healthcare system. The repercussions of those errors are more palpable in healthcare and more so in the operative microsurgical theater. The surgical microscope, although a key element within it, has a high propensity for errors. The two communication approaches evaluated in this study took advantage of the natural physiology of the human body by tracking and utilizing eye movements and body gestures to execute tasks that would typically require manual interaction with the microscope. Independent trials at the Charité Hospital in Berlin were conducted, and different technological tools like Virtual Reality were utilized to evaluate them. Specialized tasks were created for both of the trials. The results showed us that these body tracking approaches (body gestures and gaze) were almost 30% and 20% faster than the contemporary alternative. In the last 20 years, the diffusion of technology within medicine has been enormous, these new patient-oriented technological approaches could be revolutionary in controlling an existing critical element within the microsurgical theater.Das Gesundheitssystem wird von einer Vielzahl medizinischer Fehler geplagt. Die Auswirkungen dieser Fehler sind im Gesundheitswesen und insbesondere im mikrochirurgischen Operationssaal am deutlichsten spürbar. Das Operationsmikroskop ist zwar ein Schlüsselelement in diesem Bereich, aber dennoch sehr fehleranfällig. Die beiden in dieser Studie untersuchten Kommunikationsansätze verwenden die natürliche Physiologie des menschlichen Körpers, indem sie Augenbewegungen und Körpergesten verfolgen und nutzen, um Aufgaben auszuführen, die normalerweise eine manuelle Interaktion mit dem Mikroskop erfordern würden. In der Charité in Berlin wurden separate Trials durchgeführt und verschiedene technische Hilfsmittel wie Virtual Reality eingesetzt, um sie zu bewerten. Für beide Trials wurden spezielle Aufgaben erstellt. Die Ergebnisse zeigten uns, dass diese Body-Tracking-Ansätze (Körpergesten und Blicke) fast 30 % bzw. 20 % schneller waren als der aktuelle Stand der Technik. In den letzten 20 Jahren hat die Technologie in der Medizin eine enorme Verbreitung erfahren; diese neuen patientenorientierten technologischen Ansätze könnten bei der Kontrolle eines bestehenden kritischen Elements im mikrochirurgischen Bereich revolutionär sein

On Optimal Family of Codes for Archival DNA Storage

DNA based storage systems received attention by many researchers. This includes archival and re-writable random access DNA based storage systems. In this work, we have developed an efficient technique to encode the data into DNA sequence by using non-linear families of ternary codes. In particular, we proposes an algorithm to encode data into DNA with high information storage density and better error correction using a sub code of Golay code. Theoretically, 115 exabytes (EB) data can be stored in one gram of DNA by our method.Comment: Supplementary file and the software DNA Cloud 2.0 is available at http://www.guptalab.org/dnacloud This is the preliminary version of the paper that appeared in Proceedings of IWSDA 2015, pp. 143--14

The S shape of a granular pile in a rotating drum

The shape of a granular pile in a rotating drum is investigated. Using Discrete Elements Method (DEM) simulations we show that the "S shape" obtained for high rotation speed can be accounted for by the friction on the end plates. A theoretical model which accounts for the effect of the end plates is presented and the equation of the shape of the free surface is derived. The model reveals a dimensionless number which quantifies the influence of the end plates on the shape of the pile. Finally, the scaling laws of the system are discussed and numerical results support our conclusions

Delta Hedging Liquidity Positions on Automated Market Makers

Liquidity Providers on Automated Market Makers generate millions of USD in transaction fees daily. However, the net value of a Liquidity Position is vulnerable to price changes in the underlying assets in the pool. The dominant measure of loss in a Liquidity Position is Impermanent Loss. Impermanent Loss for Constant Function Market Makers has been widely studied. We propose a new metric to measure Liquidity Position PNL based on price movement from the underlying assets. We show how this new metric more appropriately measures the change in the net value of a Liquidity Position as a function of price movement in the underlying assets. Our second contribution is an algorithm to delta hedge arbitrary Liquidity Positions on both uniform liquidity Automated Market Makers (such as Uniswap v2) and concentrated liquidity Automated Market Makers (such as Uniswap v3) via a combination of derivatives