arXiv subjects

Mehdi Habibi

Publications and source records attributed to Mehdi Habibi.

At least 19 recordsLinked to original sources

arXiv2025

Tunable self-emulsification via viscoelastic control of Marangoni-driven interfacial instabilities

Interfacial instabilities in multicomponent fluidic systems are widespread in nature and in industrial processes, yet controlling their dynamics remains a challenge. Here, we present a strategy to actively tune Marangoni-driven self-emulsification at liquid-liquid interfaces by harnessing fluid viscoelasticity. When a water-alcohol droplet spreads on an oil bath, a radial surface tension gradient induced by selective alcohol evaporation drives an interfacial instability, leading to the spontaneous formation of a dense two-dimensional array of "daughter" droplets. We demonstrate that introducing trace amounts of high-molecular-weight polymers, which introduces viscoelasticity, provides a robust means of controlling this process. Increasing viscoelasticity systematically suppresses the instability, resulting in a delayed onset of fragmentation and longer spreading fingers. By combining high-resolution experimental visualization and theoretical analysis, we uncover a quantitative relationship between the polymer concentration and the finger length prior to breakup. These findings establish a predictive framework for designing viscoelastic interfacial materials with programmable dynamic and offer new opportunities for surface-tension-mediated patterning, emulsification, and fluidic control in soft material systems.

cond-mat.soft↗

arXiv2024

A novel 3D food printing technique: achieving tunable porosity and fracture properties via liquid rope coiling

We present a 3D food printing (3DFP) method to create coiled structures, harnessing the liquid rope coiling effect as a rapid method of food printing with tunable fractural properties. By studying the printability and coil-forming ability of pea, carrot, and cookie dough inks, we identified optimal printing parameters to induce steady and controlled coiling, enabling the creation of coiled structures with tunable porosities using a single nozzle. Fracture profiles from post-processed coiled structures showed complex responses but presented direct correlations between the porosity and textural parameters, including hardness, brittleness, and initial stiffness. This study provides a foundation for the fabrication of coiled food structures using 3DFP and highlights its potential application in designing textural properties and a range of unique sensory experiences.

cond-mat.soft↗

arXiv2022

Yielding and Strain Stiffening in Entangled Assemblies of Frictional Granular Chains

Packings of macroscopic granular chains capture some of the essential aspects of molecular polymer systems and have been suggested as a paradigm to understand the physics on a molecular scale. However, here we demonstrate that the interparticle friction $\mu$ in granular chain packings, which has no counterpart in polymer systems, leads to a nontrivial yielding and rheological response. Based on discrete element simulations we study the nonlinear rheology of random packings of granular chains under large amplitude oscillatory shear. We find that the maximum stress and the penetration depth of the shear deformation into the material bulk are nonmonotonic functions of friction with extrema at intermediate values of $\mu$. We also show that the regularly repeated gaps between the adjacent grains, which are special to commercial granular chains, broaden the shear zone and enhance the entanglements in the system by promoting the interlocking events between chains. These topological constraints can significantly increase the degree of strain stiffening. Our findings highlight the differences between the physics of granular chain packings and molecular polymer systems.

cond-mat.soft↗

arXiv2022

Universal Transition to Wide Shear Zones in Entangled Macroscale Chains or Ropes

Macroscale chains have been proposed to give insight into the physics of molecular polymer systems. Nevertheless, understanding the rheological response of systems of quasi-one-dimensional semiflexible materials, such as bead-chain packings, is currently a great challenge. We study the nonlinear rheology of random assemblies of macroscale chains -- including steel bead chains and cooked spaghetti -- under oscillatory shear. We show that a universal transition from localized to wide shear zones occurs upon increasing the strain amplitude, for a wide range of lengths, flexibilities, and other structural parameters of the constituent elements. The critical strain amplitude coincides with the onset of strain stiffening development in the system. We obtain scaling laws for transition sharpness, shear-zone width, and stiffness enhancement as a function of chain length. Our findings suggest that the entanglements between the constituent elements strengthen when approaching the critical strain amplitude and rapidly become long range, even spanning the entire finite system for long enough chains. We show that the nonlinear rheological response is governed by the interplay between increasing stored elastic forces due to entanglements and increasing contribution of dissipation with shear rate and interlocking between chains.

cond-mat.soft↗

arXiv2022

Molecular rotors to probe the local viscosity of a polymer glass

We investigate the local viscosity of a polymer glass around its glass transition temperature using environment-sensitive fluorescent molecular rotors embedded in the polymer matrix. The rotors' fluorescence depends on the local viscosity, and measuring the fluorescence intensity and lifetime of the probe therefore allows to measure the local free volume in the polymer glass when going through the glass transition. This also allows us to study the local viscosity and free volume when the polymer film is put under an external stress. We find that the film does not flow homogeneously, but undergoes shear banding that is visible as a spatially varying free volume and viscosity.

cond-mat.soft↗

arXiv2021

An early shutdown circuit for power reduction in high-precision dynamic comparators

Dynamic comparators are an essential part of low-power analog to digital converters (ADCs) and are referred to as one of the most important building blocks in mixed mode circuits. The power consumption and accuracy of dynamic comparators directly affects the overall power consumption and effective number of bits of the ADC. In this paper, an early shutdown approach is proposed to deactivate the first stage preamplifier at the suitable time. Furthermore, a time domain offset cancellation technique is incorporated to reduce offset effects. With the proposed method power consumption can be reduced in low power high precision dynamic comparators. The proposed method has been simulated in a standard 0.18{\mu}m CMOS technology and the results confirm its effectiveness. The proposed circuit has the ability of reducing the power consumption by 21.7% in the worst case, while having little effect on the speed and accuracy in comparison with the conventional methods. The proposed comparator consumes only 47{\mu}W while operating at 500MHz. Furthermore, Monte Carlo evaluations showed that the standard deviation of the residual input referred offset was 620{\mu}V.

eess.SP↗

arXiv2021

A 0.4 V, 19 pW Subthreshold Voltage Reference Generator Using Separate Line Sensitivity and Temperature Coefficient Correction Stages

Sensor nodes and IoT systems require blocks that not only consume low power but also have good accuracy. Voltage reference generators are also considered important building blocks in sensor interface circuits. This paper presents a solution to increase the accuracy of low power subthreshold voltage generators by lowering the circuit sensitivity to temperature and supply voltage variations. The enhancement is achieved by using two separate stages for temperature coefficient (TC) and line sensitivity (LS) correction. A 0.18 {\mu}m standard CMOS process has been used for the proposed structure. The effects of parameter variations in the fabrication process are investigated using post-layout simulation and Monte Carlo analysis. In the supply voltage of 0.4 V to 2 V, an LS of 143.8 ppm/V is obtained. In typical corner conditions, the achieved TC is 7.45 ppm/{\circ}C over the temperature range of 0{\circ}C to 80{\circ}C. Due to process changes, and mainly affected by threshold voltage variations, the average TC can change to 39.2 ppm/{\circ}C. The minimum power consumption at 0{\circ}C and at a supply voltage of 0.4 V is 3.25 pW while the power consumption increases to 2.84 nW in 80{\circ}C and at the maximum supply voltage of 2 V.

eess.SP↗

arXiv2021

CNFET-based design of efficient ternary half adder and 1-trit multiplier circuits using dynamic logic

This paper presents a ternary half adder and a 1-trit multiplier using carbon nanotube transistors. The proposed circuits are designed using pass transistor logic and dynamic logic. Ternary logic uses less connections than binary logic, and less voltage changes are required for the same amount of data transmission. Carbon nanotube transistors have advantages over MOSFETs, such as the same mobility for electrons and holes, the ability to adjust the threshold voltage by changing the nanotube diameter, and less leakage power. The proposed half adder has lower power consumption, delay, and fewer transistors compared to recent ternary half adders that use similar design methods. The proposed 1-trit multiplier also has a lower delay than other designs. Moreover, these advantages are achieved over a wide supply voltage range, operating temperatures, and output loads. The design is also more robust to process variations than the nearest design in terms of PDP.

cs.ET↗

arXiv2021

Nanopore-Based DNA Sequencing Sensors and CMOS Readout Approaches

Purpose Nanopore-based molecular sensing and measurement, specifically Deoxyribonucleic acid (DNA) sequencing, is advancing at a fast pace. Some embodiments have matured from coarse particle counters to enabling full human genome assembly. This evolution has been powered not only by improvements in the sensors themselves, but also in the assisting microelectronic Complementary Metal Oxide Semiconductor (CMOS) readout circuitry closely interfaced to them. In this light, this paper reviews established and emerging nanopore-based sensing modalities considered for DNA sequencing and CMOS microelectronic methods currently being used. Design/methodology/approach Readout and amplifier circuits which are potentially appropriate for conditioning and conversion of nanopore signals for downstream processing are studied. Furthermore, arrayed CMOS readout implementations are focused on and the relevant status of the nanopore sensor technology is reviewed as well. Findings Ion channel nanopore devices have properties unique compared with other electrochemical cells. Currently biological nanopores are the only variants reported which can be used for actual DNA sequencing. The translocation rate of DNA through such pores, the current range at which these cells operate on and the cell capacitance effect, all impose the necessity of using low noise circuits in the process of signal detection. The requirement of using in-pixel low noise circuits in turn tends to impose challenges in the implementation of large size arrays. Originality/value The study presents an overview on the readout circuits used for signal acquisition in electrochemical cell arrays and investigates the specific requirements necessary for implementation of nanopore type electrochemical cell amplifiers and their associated readout electronics.

physics.ins-det↗

arXiv2021

A signed pulse-train based image processor-array for parallel kernel convolution in vision sensors

Purpose- High speed image processing is a challenging task for real-time applications such as product quality control of manufacturing lines. Smart image sensors use an array of in-pixel processors to facilitate high-speed real-time image processing. These sensors are usually used to perform the initial low-level bulk image filtering and enhancement. Design- In this paper, using pulse-width modulated signals and regular nearest neighbor interconnections, a convolution image processor is presented. The presented processor is not only capable of processing arbitrary size kernels, but the kernel coefficients can be any arbitrary positive or negative floating number. Findings- The performance of the proposed architecture is evaluated on a FPGA platform. The peak signal-to-noise ratio (PSNR) metric is used to measure the computation error for different images, filters, and illuminations. Finally, the power consumption of the circuit in different operation conditions is presented. Originality/Value- The presented processor array can be used for high speed kernel convolution image processing tasks including arbitrary size edge detection and sharpening functions which require negative and fractional kernel values.

eess.SP↗

arXiv2021

Inverted and programmable Poynting effects in metamaterials

The Poynting effect generically manifests itself as the extension of the material in the direction perpendicular to an applied shear deformation (torsion) and is a material parameter hard to design. Unlike isotropic solids, in designed structures, peculiar couplings between shear and normal deformations can be achieved and exploited for practical applications. Here, we engineer a metamaterial that can be programmed to contract or extend under torsion and undergo nonlinear twist under compression. First, we show that our system exhibits a novel type of inverted Poynting effect, where axial compression induces a nonlinear torsion. Then the Poynting modulus of the structure is programmed from initial negative values to zero and positive values via a pre-compression applied prior to torsion. Our work opens avenues for programming nonlinear elastic moduli of materials and tuning the couplings between shear and normal responses by rational design. Obtaining inverted and programmable Poynting effects in metamaterials inspires diverse applications from designing machine materials, soft robots and actuators to engineering biological tissues, implants and prosthetic devices functioning under compression and torsion.

cond-mat.soft↗

arXiv2020

Transmit Power Optimization in Optical Coherent Transmission Systems: Analytical, Simulation, and Experimental Results

In this paper, we propose to use the discretized version of the so-called Enhanced Gaussian Noise (EGN) model to estimate the non-linearity effects of fiber on the performance of optical coherent and uncompensated transmission (CUT) systems. By computing the power of non-linear interference noise and considering optical amplifier noise, we obtain the signal-to-noise (SNR) ratio and achievable rate of CUT. To allocate the power of each CUT channel, we consider two optimization problems with the objectives of maximizing minimum SNR margin and achievable rate. We show that by using the discretized EGN model, the complexity of the introduced optimization problems is reduced compared with the existing optimization problems developed based on the so-called discretized Gaussian Noise (GN) model. In addition, the optimization based on the discretized EGN model leads to a better SNR and achievable rate. We validate our analytical results with simulations and experimental results. We simulate a five-channel coherent system on OptiSystem software, where a close agreement is observed between optimizations and simulations. Furthermore, we measured SNR of commercial 100Gbps coherent transmitter over 300 km single-mode fiber (SMF) and non-zero dispersion-shifted fiber (NZDSF), by considering single-channel and three-channel coherent systems. We observe there are performance gaps between experimental and analytical results, which is mainly due to other sources of noise such as transmitter imperfection noise, thermal noise, and shot noise, in experiments. By including these sources of noise in the analytical model, the gaps between analytical and experimental results are reduced.

eess.SP↗

arXiv2019

A Range Matching CAM for Hierarchical Defect Tolerance Technique in NRAM Structures

Due to the small size of nanoscale devices, they are highly prone to process disturbances which results in manufacturing defects. Some of the defects are randomly distributed throughout the nanodevice layer. Other disturbances tend to be local and lead to cluster defects caused by factors such as layer misintegration and line width variations. In this paper, we propose a method for identifying cluster defects from random ones. The motivation is to repair the cluster defects using rectangular ranges in a range matching content-addressable memory (RM-CAM) and random defects using triple-modular redundancy (TMR). It is believed a combination of these two approaches is more effective for repairing defects at high error rate with less resource. With the proposed fault repairing technique, defect recovery results are examined for different fault distribution scenarios. Also the mapping circuit structure required for two conceptual 32*32 and 64*64 bit RAMs are presented and their speed, power and transistor count are reported.

cs.AR↗

arXiv2018

The normal yield stress

Normal stresses in complex fluids lead to new flow phenomena because they can be comparable to or even larger than the shear stress itself. In addition, they are of paramount importance for formulating and testing constitutive equations for predicting non-viscometric flow behavior. Very little attention has so far been paid to the normal stresses of yield stress fluids, mainly because they are very difficult to measure. We report the first systematic study of the first and second normal stress differences, N1 (>0) and N2 (<0), in both continuous and oscillatory shear of three model yield stress fluids. We show that both normal stress differences are quadratic functions of the shear stress both above and below the shear yield stress, leading to the existence of a yield normal stress.

cond-mat.soft↗

arXiv2017

Compaction of Quasi One-Dimensional Elastoplastic Materials

Insight in the crumpling or compaction of one-dimensional objects is of great importance for understanding biopolymer packaging and designing innovative technological devices. By compacting various types of wires in rigid confinements and characterizing the morphology of the resulting crumpled structures, here we report how friction, plasticity, and torsion enhance disorder, leading to a transition from coiled to folded morphologies. In the latter case, where folding dominates the crumpling process, we find that reducing the relative wire thickness counter-intuitively causes the maximum packing density to decrease. The segment-size distribution gradually becomes more asymmetric during compaction, reflecting an increase of spatial correlations. We introduce a self-avoiding random walk model and verify that the cumulative injected wire length follows a universal dependence on segment size, allowing for the prediction of the efficiency of compaction as a function of material properties, container size, and injection force.

cond-mat.soft↗

arXiv2016

Effect of plasticity and dimensionality on crumpling of a thin sheet

The process of crumpling a sheet and compacting it into a ball is dependent on many parameters that are difficult to disentangle. We study the effect of plasticity on the crumpling process, and disentangle the effects of plasticity and dimensionality of compaction by performing isotropic compaction experiments on various materials with different elastoplasticities. The force required to crumple a sheet into a ball as well as the number of layers inside the ball have a power-law dependence on the size of the crumpled ball, each with its own power-law exponent. We experimentally determine both exponents and find that they are linearly proportional to and decrease with increasing plasticity of the material. Finally we provide a scaling argument predicting a linear relation between the two exponents with a coefficient of 3.5 in excellent agreement with our experimental results.

cond-mat.soft↗

arXiv2015

Nonmonotonic fracture behavior of polymer nanocomposites

Polymer composite materials are widely used for their exceptional mechanical properties, notably their ability to resist large deformations. Here we examine the failure stress and strain of rubbers reinforced by varying amounts of nano-sized silica particles. We find that small amounts of silica increase the fracture stress and strain, but too much filler makes the material become brittle and consequently fracture happens at small deformations. We thus find that as a function of the amount of filler there is an optimum in the breaking resistance at intermediate filler concentrations. We use a modified Griffith theory to establish a direct relation between the material properties and the fracture behavior that agrees with the experiment.

cond-mat.soft↗

arXiv2014

Granular transport in a horizontally vibrated sawtooth channel

We present a new mode of transport of spherical particles in a horizontally vibrated channel with sawtooth shaped side walls. The underlying driving mechanism is based on an interplay of directional energy injection transformed by the sidewall collisions and density dependent interparticle collisions. Experiments and matching numerics show that the average particle velocity reaches a maximum at 60% of the maximal filling density. Introducing a spatial phase shift between the channel boundaries increases the transport velocity by an order of magnitude.

cond-mat.stat-mech↗