Experimental Mobility Data Research Articles

A mobility-based deployment strategy for edge data centers

The main objective of Multi-access Edge Computing (MEC) is to bring computational capabilities at the edge of the network to better support low-latency applications. Such capabilities are typically offered by Edge Data Centers (EDC). The MEC paradigm is not tied to a single radio technology, rather it embraces both cellular and other radio access technologies such as WiFi. Distributed intelligence at the edge for AI purposes requires careful spatial planning of computing and storage resources. The problem of EDC deployment in urban environments is challenging and, to the best of our knowledge, it has been explored only for cellular connectivity so far. In this paper, we study the possibility of deploying EDC without analyzing the expected data traffic load of the cellular network, a kind of information rarely shared by network operators. To this purpose, we propose in this work CLUB, CLUstering-Based strategy tailored on the analysis of urban mobility. We analyze two experimental mobility data sets, and we analyze some mobility features in order to characterize their properties. Finally, we compare the performance of CLUB against state-of-the-art techniques in terms of the outage probability, namely the probability an EDC is not able to serve a request. Our results show that the CLUB strategy is always comparable with respect to our benchmarks, but without using any information related to network traffic.

Zeta Potential and Colloidal Stability Predictions for Inorganic Nanoparticle Dispersions: Effects of Experimental Conditions and Electrokinetic Models on the Interpretation of Results

In this work, a set of experimental electrophoretic mobility (μe) data was used to show how inappropriate selection of the electrokinetic model used to calculate the zeta potential (ζ-potential) can compromise the interpretation of the results for nanoparticles (NPs). The main consequences of using ζ-potential values as criteria to indicate the colloidal stability of NP dispersions are discussed based on DLVO interaction energy predictions. For this, magnetite (Fe3O4) NPs were synthesized and characterized as a model system for performing electrokinetic experiments. The results showed that the Fe3O4 NPs formed mass fractal aggregates in solution, so the ζ-potential could not be determined under ideal conditions when μe depends on the NP radius. In addition, the Dukhin number (Du) estimated from potentiometric titration results indicated that stagnant layer conduction (SLC) could not be neglected for this system. The electrokinetic models that do not consider SLC grossly underestimated the ζ-potential values for the Fe3O4 NPs. The DLVO interaction energy predictions for the colloidal stability of the Fe3O4 NP dispersions also depended on the electrokinetic model used to calculate the ζ-potential. The results obtained for the Fe3O4 NP dispersions also suggested that, contrary to many reports in the literature, high ζ-potential values do not necessarily reflect high colloidal stability for charge-stabilized NP dispersions.

Universal mobility characteristics of graphene originating from charge scattering by ionised impurities

Pristine graphene and graphene-based heterostructures can exhibit exceptionally high electron mobility if their surface contains few electron-scattering impurities. Mobility directly influences electrical conductivity and its dependence on the carrier density. But linking these key transport parameters remains a challenging task for both theorists and experimentalists. Here, we report numerical and analytical models of carrier transport in graphene, which reveal a universal connection between graphene’s carrier mobility and the variation of its electrical conductivity with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which is verified by numerical solution of the Boltzmann transport equation including the effects of charged impurity scattering and optical phonons on the carrier mobility. This model reproduces, explains, and unifies experimental mobility and conductivity data from a wide range of samples and provides a way to predict a priori all key transport parameters of graphene devices. Our results open a route for controlling the transport properties of graphene by doping and for engineering the properties of 2D materials and heterostructures.

Electron mobility of strained InGaAs long-channel MOSFETs: From scattering rates to TCAD model

TCAD modelling of InGaAs channel MOSFETs is a complex task due to the combined effect of quantization and interface or border traps, which affect the device electrostatics as well as the electron mobility through Coulomb scattering. In addition, trap distributions and mobility are strain-dependent. In this paper, we start from a microscopic physical approach, based on the use of Sentaurus SBand by Synopsys as 1D Schrödinger-Poisson solver and mobility calculator through the Kubo-Greenwood (KG) approach, to end up with a TCAD modelling framework that combines the Density Gradient (DG) model for quantum corrections with simple empirical expressions for the mobility model. Only the long-channel (or low-field) mobility is addressed. A distinctive feature of the paper is the use of experimental Hall electron density and mobility data as a reference for the calibration of interface traps and scattering rates in SBand. SBand simulation results for different strain levels and layer thicknesses are then used as the basis for the TCAD model calibration (DG and mobility). Our findings indicate that strain can increase mobility mainly through the reduction of Coulomb scattering with trapped charge.

Determination of thermodynamic acidity constants and limiting ionic mobilities of weak electrolytes by capillary electrophoresis using a new free software AnglerFish.

Thermodynamic acidity constants (acid or acid-base dissociation constants, sometimes called also as ionization constants) and limiting ionic mobilities (both of them at defined temperature, usually 25°C) are the fundamental physicochemical characteristics of a weak electrolyte, that is, weak acid or weak base or ampholyte. We introduce a novel method for determining the data of a weak electrolyte by the nonlinear regression of effective electrophoretic mobility versus buffer composition dependence when measured in a set of BGEs with various pH. To correct the experimental data for zero ionic strength we use the extended Debye-Hückel model and Onsager-Fuoss law with no simplifications. Contrary to contemporary approaches, the nonlinear regression is performed on limiting mobility data calculated by PeakMaster's correction engine, not on the raw experimental mobility data. Therefore, there is no requirement to perform all measurements at a constant ionic strength of the set of BGEs. We devised the computer program AnglerFish that performs the necessary calculations in a user-friendly fashion. All thermodynamic pKa values and limiting electrophoretic mobilities for arbitrarily charged substances having any number of ionic forms are calculated by one fit. The user input consists of the buffer composition of the set of BGEs and experimentally measured effective mobilities of the inspected weak electrolyte.

Nanoparticles in dilute gases: Fundamental equivalence between momentum accommodation and surface adsorption.

Momentum accommodation is a key factor governing the transport of particles in gases from electric mobility and Brownian diffusion to thermophoresis. This paper explores the relationship between momentum accommodation of nanoparticles in dilute gases and surface adsorption. We demonstrate that the momentum accommodation factor is fundamentally equal to the probability of surface adsorption. Molecular dynamics simulations show that surface adsorption is the key mechanism behind the diffuse scattering model, and that upon gas-particle collision the immediate reflection dynamics and surface adsorption events are governed by the kinetic energy distribution of the rebounding gas molecules. This distribution determines the transition of the dominant mode of molecular scattering off a particle surface from diffuse to specular elastic reflection as the particle approaches the realm of molecular size. The kinetics and equilibrium of physisorption are examined to shed light on the effect of the lifetime of surface adsorbates on momentum transfer. A statistical treatment is proposed for the adsorption and hence the gas-nanoparticle momentum accommodation coefficient. The validity of the theoretical treatment is examined by comparing its prediction against experimental mobility data of silver nanoparticles.

A set of cross sections and transport coefficients for CF3+ ions in CF4

A cross section set for CF3+ ions in CF4 gas has been assembled from the available experimental and theoretical data using a swarm method. Elastic cross section consistent with the available experimental mobility data has been derived and the set also includes the reactive cross sections. Reactive rates are deduced for collision energies of up to 500 eV. The transport properties of CF3+ ions in CF4 gas in DC (direct current) electric field fields at a gas temperature of T = 300 K were calculated as a function of the reduced electric field E/N (E is electric field and N is gas number density) by using a Monte Carlo simulation. The non-conservative collisions are also taken into account in the definition of transport coefficients.

Enhanced thermoelectric performance in single-crystal-like semiconducting flexible GaAs films

With the advancement of nano-technology and push toward flexible electronics, the opportunity to generate electricity using solid-state devices has ushered tremendous research interest in improving the thermoelectric (TE) properties of flexible semiconducting materials. The majority of research done so far was focused on finding suitable doping schemes for all-organic flexible substrates or mixing organic and inorganic components to obtain flexible substrates with an optimized thermoelectric performance. Unfortunately, their performance is limited by their low power factor (PF) values and often suffers from degradation issues due to the organic component that limits them to low temperature applications. Here, through coupled microstructural and thermoelectric analysis, we show how to overcome these limitations by introducing a new inorganic GaAs flexible substrate with enhanced TE performance. We show that these flexible thin films are single-crystal-like biaxially textured with low angle grain boundary misalignment; and charge transport is dominated by multi- valley electron conduction. This results in a PF ∼1300 µW/mK2, the highest value for non-toxic inorganic flexible thin films and an estimated 3-fold enhancement in the figure of merit compared with bulk GaAs. We present the temperature-dependent experimental PF, mobility, and carrier concentration data coupled with the theoretical models to elucidate the charge transport characteristics of this new class of films. Moreover, these unique charge transport characteristics are material growth dependent, and thus, such novel thermoelectric properties are expected in different material systems.

Hydrodynamic mobility of confined polymeric particles, vesicles, and cancer cells in a square microchannel.

The transport of deformable objects, including polymer particles, vesicles, and cells, has been a subject of interest for several decades where the majority of experimental and theoretical studies have been focused on circular tubes. Due to advances in microfluidics, there is a need to study the transport of individual deformable particles in rectangular microchannels where corner flows can be important. In this study, we report measurements of hydrodynamic mobility of confined polymeric particles, vesicles, and cancer cells in a linear microchannel with a square cross-section. Our operating conditions are such that the mobility is measured as a function of geometric confinement over the range 0.3 < λ < 1.5 and at specified particle Reynolds numbers that are within 0.1 < Rep < 2.5. The experimental mobility data of each of these systems is compared with the circular-tube theory of Hestroni, Haber, and Wacholder [J. Fluid Mech. 41, 689-705 (1970)] with modifications made for a square cross-section. For polymeric particles, we find that the mobility data agrees well over a large confinement range with the theory but under predicts for vesicles. The mobility of vesicles is higher in a square channel than in a circular tube, and does not depend significantly on membrane mechanical properties. The mobility of cancer cells is in good agreement with the theory up to λ ≈ 0.8, after which it deviates. Comparison of the mobility data of the three systems reveals that cancer cells have higher mobility than rigid particles but lower than vesicles, suggesting that the cell membrane frictional properties are in between a solid-like interface and a fluid bilayer. We explain further the differences in the mobility of the three systems by considering their shape deformation and surface flow on the interface. The results of this study may find potential applications in drug delivery and biomedical diagnostics.

Improved surface-roughness scattering and mobility models for multi-gate FETs with arbitrary cross-section and biasing scheme

We present a new model for surface roughness (SR) scattering in n-type multi-gate FETs (MuGFETs) and gate-all-around nanowire FETs with fairly arbitrary cross-sections, its implementation in a complete device simulator, and the validation against experimental electron mobility data. The model describes the SR scattering matrix elements as non-linear transformations of interface fluctuations, which strongly influences the root mean square value of the roughness required to reproduce experimental mobility data. Mobility simulations are performed via the deterministic solution of the Boltzmann transport equation for a 1D-electron gas and including the most relevant scattering mechanisms for electronic transport, such as acoustic, polar, and non-polar optical phonon scattering, Coulomb scattering, and SR scattering. Simulation results show the importance of accounting for arbitrary cross-sections and biasing conditions when compared to experimental data. We also discuss how mobility is affected by the shape of the cross-section as well as by its area in gate-all-around and tri-gate MuGFETs.

Drag force and transport property of a small cylinder in free molecule flow: A gas-kinetic theory analysis.

Analytical expressions are derived for aerodynamic drag force on small cylinders in the free molecule flow using the gas-kinetic theory. The derivation considers the effect of intermolecular interactions between the cylinder and gas media. Two limiting collision models, specular and diffuse scattering, are investigated in two limiting cylinder orientations with respect to the drift velocity. The earlier solution of Dahneke [B. E. Dahneke, J. Aerosol Sci. 4, 147 (1973)10.1016/0021-8502(73)90066-9] is shown to be a special case of the current expressions in the rigid-body limit of collision. Drag force expressions are obtained for cylinders that undergo Brownian rotation and for those that align with the drift velocity. The validity of the theoretical expressions is tested against experimental mobility data available for carbon nanotubes.

Transcript Abundance Explains mRNA Mobility Data in Arabidopsis thaliana.

Recently, a large population of mRNA was shown to be able to travel between plant organs via sieve elements as a putative long-distance signaling molecule. However, a mechanistic basis by which transcripts are selected for transport has not yet been identified. Here, we show that experimental mRNA mobility data in Arabidopsis can be explained by transcript abundance and half-life. This suggests that the majority of identified mobile transcripts can be accounted for by non-sequence-specific movement of mRNA from companion cells into sieve elements.

Coherent quantum transport in disordered systems: A unified polaron treatment of hopping and band-like transport.

Quantum transport in disordered systems is studied using a polaron-based master equation. The polaron approach is capable of bridging the results from the coherent band-like transport regime governed by the Redfield equation to incoherent hopping transport in the classical regime. A non-monotonic dependence of the diffusion coefficient is observed both as a function of temperature and system-phonon coupling strength. In the band-like transport regime, the diffusion coefficient is shown to be linearly proportional to the system-phonon coupling strength and vanishes at zero coupling due to Anderson localization. In the opposite classical hopping regime, we correctly recover the dynamics described by the Fermi's Golden Rule and establish that the scaling of the diffusion coefficient depends on the phonon bath relaxation time. In both the hopping and band-like transport regimes, it is demonstrated that at low temperature, the zero-point fluctuations of the bath lead to non-zero transport rates and hence a finite diffusion constant. Application to rubrene and other organic semiconductor materials shows a good agreement with experimental mobility data.

Theoretical predictor for candidate structure assignment from IMS data of biomolecule-related conformational space.

The ability to correlate experimental ion mobility data with candidate structures from theoretical modeling provides a powerful analytical and structural tool for the characterization of biomolecules. In the present paper, a theoretical workflow is described to generate and assign candidate structures for experimental trapped ion mobility and H/D exchange (HDX-TIMS-MS) data following molecular dynamics simulations and statistical filtering. The applicability of the theoretical predictor is illustrated for a peptide and protein example with multiple conformations and kinetic intermediates. The described methodology yields a low computational cost and a simple workflow by incorporating statistical filtering and molecular dynamics simulations. The workflow can be adapted to different IMS scenarios and CCS calculators for a more accurate description of the IMS experimental conditions. For the case of the HDX-TIMS-MS experiments, molecular dynamics in the "TIMS box" accounts for a better sampling of the molecular intermediates and local energy minima.

Empirical Model for the Effective Electron Mobility in Silicon Nanowires

An empirical model for the effective electron mobility in silicon nanowires (SiNWs) is presented. The model is based on published mobility data from numerical simulations of electron transport in SiNWs with different cross sections. Both phonon scattering and surface roughness scattering as well as the impact of the effective vertical field are considered. A comparison with a variety of experimental mobility data from the literature shows that the model can be treated as a reference for benchmarking different NW technologies. The effective field dependence is modeled by a simple expression making our mobility model very efficient for the use in numerical device simulators or in analytical MOSFET models.

Dynamics and drift motion of O2− in supercritical argon

A method is presented for the study of the mean motion and the dynamics of ions under the action of an electrostatic field in supercritical fluids through a nonequilibrium molecular dynamics simulation technique. In the case of O2− in Ar, the ion–neutral interaction potential is determined through the reproduction of the experimental mobility data. This enabled the prediction of the radial distribution around the ion and the dynamics of the ion motion. In addition, the diffusion coefficient components, parallel and perpendicular to the electric field, have been calculated and found to be almost equal to one another and to depend weakly to the Ar density. The appearance of a shell around an ion is confirmed and found to be strengthened with density increase. The method has been applied at moderate Ar densities and low field strengths but can be extended to denser systems and stronger field strengths at the expense of high amounts of computer time.

Finite element simulation of the behavior of the periodontal ligament: A validated nonlinear contact model

Due to its significance in tooth movement, the stress/deformation field of periodontium and the alveolar bone remodeling process, periodontal ligament (PDL) cannot be excluded from the studies investigating dental biomechanics regarding its excessive deformability. Therefore, many analytical and numerical researches are carried out to simulate its response and to create a constitutive model via experiments intending to discover the material properties of PDL. The aim of this study is to formulate a user specified contact model that can be used in conjunction with finite element (FE) software and reflects PDL’s influence on neighboring structures based on the currently available information, without requiring an actual volumetric finite element mesh of ligament. The results show good agreement with available experimental tooth mobility data. Smooth stress fields are obtained on the tooth root and alveolar bone, which is a significant aspect in bone-remodeling studies. The advantage of simulating PDL as a contact model at the interface of tooth root and the alveolar process instead of a solid-meshed FE model with poor geometric morphology and/or very dense mesh is expected to save pre/post-processing workforce, to increase the accuracy and to contribute to the smoothness of interface stress distributions.

Equivalence of donor and acceptor fits of temperature dependent Hall carrier density and Hall mobility data: Case of ZnO

In this work, statistical formulations of the temperature dependence of ionized and neutral impurity concentrations in a semiconductor, needed in the charge balance equation and for carrier scattering calculations, have been developed. These formulations have been used in order to elucidate a confusing situation, appearing when compensating acceptor (donor) levels are located sufficiently close to the conduction (valence) band to be thermally ionized and thereby to emit (capture) an electron to (from) the conduction (valence) band. In this work, the temperature dependent Hall carrier density and Hall mobility data adjustments are performed in an attempt to distinguish the presence of a deep acceptor or a deep donor level, coexisting with a shallower donor level and located near the conduction band. Unfortunately, the present statistical developments, applied to an n-type hydrothermal ZnO sample, lead in both cases to consistent descriptions of experimental Hall carrier density and mobility data and thus do not allow to determine the nature, donor or acceptor, of the deep level. This demonstration shows that the emission of an electron in the conduction band, generally assigned to a (0/+1) donor transition from a donor level cannot be applied systematically and could also be attributed to a (−1/0) donor transition from an acceptor level. More generally, this result can be extended for any semiconductor and also for deep donor levels located close to the valence band (acceptor transition).

Mass Spectrometry Defines the C-Terminal Dimerization Domain and Enables Modeling of the Structure of Full-Length OmpA

The transmembrane domain of the outer membrane protein A (OmpA) from Escherichia coli is an excellent model for structural and folding studies of β-barrel membrane proteins. However, full-length OmpA resists crystallographic efforts, and the link between its function and tertiary structure remains controversial. Here we use site-directed mutagenesis andmass spectrometry of different constructs of OmpA, released in the gas phase from detergent micelles, to define the minimal region encompassing the C-terminal dimer interface. Combining knowledge of the location of the dimeric interface with molecular modeling and ion mobility data allows us to propose a low-resolution model for the full-length OmpA dimer. Our model of the dimer is in remarkable agreement with experimental ion mobility data, with none of the unfolding or collapse observed for full-length monomeric OmpA, implying that dimer formation stabilizes the overall structure and prevents collapse of the flexible linker that connects the two domains.

Electrophoretic mobility of sarcoplasmic reticulum vesicles — Analytical model includes amino acid residues of A + P + N domain of Ca2 +-ATPase and charged lipids

This work is an experimental and theoretical study of electrostatic and hydrodynamic properties of the surface of sarcoplasmic reticulum (SR) membrane using particle electrophoresis. The essential structural components of SR membrane include a lipid matrix and a dense layer of Ca2+-ATPases embedded in the matrix. The Ca2+-ATPase layer both drives and impedes vesicle mobility. To analyze the experimental mobility data, obtained at pH4.0, 4.7, 5.0, 6.0, 7.5, and 9.0 in 0.1M monovalent (1:1) electrolyte, an analytical solution for the vesicle mobility and electroosmotic flow velocity distribution was obtained by solving the Poisson–Boltzmann and the Navier–Stokes–Brinkman equations. The electrophoretic mobility model includes two sets of charges that represent: (a) charged lipids of the lipid matrix of the vesicle core, and (b) charged amino acid residues of APN domains of Ca2+-ATPases. APN domains are assumed to form a charged plane displaced from the surface of lipid matrix. The charged plane is embedded in a frictional layer that represents the surface layer of calcium pumps. Electrophoretic mobility is driven by the charged APN domain and by lipid matrix while the surface layer provides hydrodynamic friction. The charge of APN domain is determined by ionized amino acid residues obtained from the amino acid composition of SERCA1a Ca2+-ATPase. Agreement between the measured and the predicted mobility is evaluated by the weighted sum of mobility deviation squared. This model reproduces the experimental dependence of mobility on pH and predicts that APN domains are located in the upper half of the SR vesicle surface layer.