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E. Altshuler

Publications and source records attributed to E. Altshuler.

At least 19 recordsLinked to original sources

Effect of the repulsion between twin granular impactors on crater's aspect ratio: preliminary findings

We study the role of repulsive granular interactions between identical intruders as they impact a granular bed. We demonstrate experimentally that repulsion does have a measurable effect in the aspect ratio of binary craters. Furthermore, we show that the protocol followed for the preparation of the granular bed plays a crucial role in the output of table-top experiments on doublet craters.

cond-mat.soft

yupi: Generation, Tracking and Analysis of Trajectory data in Python

The study of trajectories is often a core task in several research fields. In environmental modelling, trajectories are crucial to study fluid pollution, animal migrations, oil slick patterns or land movements. In this contribution, we address the lack of standardization and integration existing in current approaches to handle trajectory data. Within this scenario, challenges extend from the extraction of a trajectory from raw sensor data to the application of mathematical tools for modeling or making inferences about populations and their environments. This work introduces a generic framework that addresses the problem as a whole, i.e., a software library to handle trajectory data. It contains a robust tracking module aiming at making data acquisition handy, artificial generation of trajectories powered by different stochastic models to aid comparisons among experimental and theoretical data, a statistical kit for analyzing patterns in groups of trajectories and other resources to speed up pre-processing of trajectory data. It is worth emphasizing that this library does not make assumptions about the nature of trajectories (e.g., those from GPS), which facilitates its usage across different disciplines. We validate the software by reproducing key results when modelling dynamical systems related to environmental modelling applications. An example script to facilitate reproduction is presented for each case.

stat.CO

Sink versus tilt penetration into shaken dry granular matter: The role of the foundation

We study the behavior of cylindrical objects as they sink into a drygranular bed fluidized due to lateral oscillations. Somewhat unexpectedly, we have found that, within a large range of lateral shaking powers,cylinders with flat bottoms sink vertically, while those with a''foundation'' consisting in ashallow ring attached to their bottom, tilt besides sinking. Thelatter scenario seems to dominate independently from the nature ofthe foundation when strong enough lateral vibrations are applied. Weare able to explain the observed behavior by quasi-2D numericalsimulations, which also demonstrate the influence of the intruder's aspect ratio. The vertical sink dynamics is explained with the help of a Newtonian equation of motion for the intruder. Our findings may shed light on the behavior of buildings and other man-made constructions during earthquakes.

physics.geo-ph

Continuous to intermittent flows in growing granular heaps

If a granular material is poured from above on a horizontal surface between two parallel, vertical plates, a sand heap grows in time. For small piles, the grains flow smoothly downhill, but after a critical pile size $X_c$, the flow becomes intermittent: sudden avalanches slide downhill from the apex to the base, followed by an "uphill front" that slowly climbs up, until a new downhill avalanche interrupts the process. By means of experiments controlling the distance between the apex of the sandpile and the container feeding it from above, we show that $X_c$ grows linearly with the input flux, but scales as the square root of the feeding height. We explain these facts based on a phenomenological model based on the experimental observation that the flowing granular phase forms a "wedge" on top of the static one, differently from the case of stationary heaps. Moreover, we demonstrate that our controlled experiments allow to predict the value of $X_c$ for the common situation in which the feeding height decreases as the pile increases in size.

cond-mat.soft

Experiments in the penetration of cuboid intruders near walls into granular matter

When an object penetrates into granular matter near a boundary, it experiences a horizontal repulsion due to the intruder-grain-wall interaction. Here we show experimentally that a square cuboid intruder, released from rest with no initial velocity, neara vertical wall to its left, goes through three distinct kinds of motion: it first tilts clockwise, then 'slides' away from the wall,and finally tilts counterclockwise. This dynamic highly favors both repulsion and penetration of the cuboid intruder as compared to that observed from its release farther away from the wall

cond-mat.soft

Intruders cooperatively interact with a wall into granular matter

When a cylindrical object penetrates granular matter near a vertical boundary, it experiences two effects: its center of mass moves horizontally away from the wall, and it rotates around its symmetry axis. Here we show experimentally that, if two identical intruders instead of one are released side-by-side near the wall, both effects are also detected. However, unexpected phenomena appear due to a cooperative dynamics between the intruders. The net horizontal distance traveled by the common center of mass of the twin intruders is much larger than that traveled by one intruder released at the same initial distance from the wall, and the rotation is also larger. The experimental results are well described by the Discrete Element Method, which reveals a further unexpected phenomenon: when four intruders are released as a column near a wall, they penetrate like a chain that "bends away" from the wall so its lower end is very strongly repelled away from it.

cond-mat.soft

Protecting others vs. protecting yourself against ballistic droplets: Quantification by stain patterns

It is often accepted a priori that a face mask worn by an infected subject is effective to avoid the spreading of a respiratory disease, while a healthy person is not necessarily well protected when wearing the mask. Using a frugal stain technique, we quantify the ballistic droplets reaching a receptor from a jet-emitting source which mimics a coughing, sneezing or talking human: in real life, such droplets may host active SARS-CoV-2 virus able to replicate in the nasopharynx. We demonstrate that materials often used in home-made face masks block most of the droplets. We also show quantitatively that less liquid carried by ballistic droplets reaches a receptor when a blocking material is deployed near the source than when located near the receptor, which supports the paradigm that your face mask does protect you, but protects others even better than you.

physics.med-ph

Design of an Externally Driven Current Cloak

An inhomogeneity into a conductive matrix deforms the flow pattern of an applied electric current. A usual current cloak can be defined as a permanent modification of the matrix properties around the inhomogeneity guaranteeing that the current flow pattern is similar before and after passing by the modified zone, so it implies the "electrical invisibility" of the inhomogeneous region. Here we introduce the concept of a current cloak that can be tuned --switched on and off, for example-- by means on an external field. We demonstrate analytically and using Finite Elements Simulations that a current cloak can be constructed and manipulated by an external magnetic field for a concrete system consisting in a magneto-resistive matrix with a stainless steel inclusion.

physics.app-ph

Following in the footsteps of E. coli: sperm in microfluidic "strictures"

We briefly describe the similarities of the experiments of sperm motion in microfluidic "strictures" by Zafeeani et al. in 2019 (Sci. Adv. 5, eaav21111, 2019) and those by Altshuler et al. in 2013 (Soft Matter 9, 1864, 2013). We shortly discuss the hydrodynamic elements justifying the strong resemblance between the two types of experiments, and suggest that other previous results in E. coli motion (Soft Matter 11, 6248, 2015) may shed further light on the understanding of sperm migration.

cond-mat.soft

Log-normal Superstatistics Reveals Statistical Resilience in the Panic Response of Confined Ants

We report the emergence of Log-normal Superstatistics in the collective motion of ants confined in a quasi-2D arena and exposed to a panic-inducing stimulus. A data-driven superstatistical Langevin model accurately reproduces the transition from stationary behavior to an organized escape response, characterized by non-Gaussian velocity distributions and a stochastic diffusion coefficient. Our findings show that danger information propagates via a memory-limited, cascade-like mechanism, resulting in a stable cluster formation despite individual memory constraints. These results indicate that a slowly varying diffusivity arises from the multiplicative combination of interaction-mediated processes under confinement, leading naturally to Log-normal fluctuations. The persistence of this statistical structure under panic reveals a form of collective resilience, establishing a mechanistic bridge between Superstatistics and living active matter in confined environments.

q-bio.PE

An autonomous robot for continuous tracking of millimetric-sized walkers

The precise and continuous tracking of millimetric-sized walkers --such as ants-- is quite important in behavioral studies. However, due to technical limitations, most studies concentrate on trajectories within arenas no more than 100 times bigger than the size of the walker or longer trajectories at the expense of either accuracy or continuity. Our work describes a scientific instrument designed to push the boundaries of precise and continuous motion analysis up to 1000 body lengths or more. It consists of a mobile robotic platform that uses Digital Image Processing techniques to track the targets in real time by calculating their spatial position. During the experiments, all the images are stored, and afterwards processed to estimate with higher precision the path traced by the walkers. Some preliminary results achieved using the proposed tracking system are presented.

physics.bio-ph

Optics undergraduate experiments using smart (and not so smart) phones

Smartphones may be seen as miniature toolboxs to perform Physics experiments. In this paper, we present three different "optics workbenches" mainly based on the light meter of a smartphone. One is aimed at the precise study of Malus law and other effects associated to linearly polarized light, the second allows quantifying the light intensity distribution of diffraction or interference patterns projected on a screen, and the third demonstrates the so-called inverse square law obeyed by the light from a pointlike source. These experiments allow to quantitatively demonstrate three fundamental laws of optics using quite inexpensive equipment.

physics.ed-ph

Intermittent and continuos flows in granular piles: effects of controlling the feeding height

Using a specially designed experimental set up, we have studied the so-called continuous to intermittent flow transition in sand piles confined in a Hele-Shaw cell where the deposition height of the sand can be controlled. Through systematic measurements varying the height and the input flow, we have established, for the first time, how the size of the pile at which the transition takes place depends on the two parameters studied. The results obtained allows to explain, at least semi-quantitatively, the observations commonly reported in the literature, carried out in experiments where the deposition height is not controlled.

cond-mat.soft

Planetary gravities on a low budget: sample test of a Mars rover wheel

We introduce an instrument for a wide spectrum of experiments on gravities other than our planet's. It is based on a large Atwood machine where one of the loads is a bucket equipped with a single board computer and different sensors. The computer is able to detect the falling (or rising) and then the stabilization of the effective gravity and to trigger actuators depending on the experiment. Gravities within the range 0.4 g to 1.2 g are easily achieved with acceleration noise of the order of 0.01 g. Under Martian gravity we are able to perform experiments of approximately 1.5 seconds duration. The system includes features such as WiFi and a web interface with tools for the setup, monitor and the data analysis of the experiment. We briefly show a case study in testing the performance of a model Mars rover wheel in low gravities.

astro-ph.IM

Preliminary quantification of freely exploring Atta insularis

In this paper, we study the "free exploration" of individual ants of the species Atta insularis, i.e., their motion on a featureless flat, horizontal surface. Two basic preliminary results emerge from our work (a) the free exploration is super-diffusive and (b) ants tend to turn more frequently to the left than to the right -so we call them "let-handed"-. More statistics is needed, however, to confirm those findings.

q-bio.QM

Intruder penetration into granular matter studied by Lock-in Accelerometry

Understanding the penetration dynamics of intruders in granular beds is relevant not only for fundamental physics, but also for geophysical processes and construction on sediments or granular soils in areas potentially affected by earthquakes. In this work, we use Lock-in accelerometry to study the penetration of intruders into quasi-2D granular matter fluidized by lateral shaking. We observed that there are two well-defined stages in the penetration dynamics as the intruder sinks into the granular material.

cond-mat.soft

Inverted anisotropy in the in-plane dissipation of BSCCO tapes: preliminary results

The electrical properties of superconducting tapes and coatings in the direction transverse to the long dimension of the composite has been rarely studied. However, transverse dissipation can eventually determine the behavior of a transmission line in the case of failure due to the presence of transversal cracks, and is also fundamental in the AC regime. In this paper we present a preliminary experimental study of the electrical transport properties along the transverse direction of BSCCO-metal tapes, and compare them with those measured along the long axis of the material. In spite of the fact that the tapes under study are not multi-filamentary, our experiments suggest that there is a measurable anisotropy of the transport properties between the longitudinal and transverse directions.

cond-mat.supr-con