Negative Mobility Research Articles

Effect of Temperature and Electric Field Strength on Carrier Mobility of Oil-Impregnated Pressboard Under DC Voltage

The influence of carrier mobility on the space charge transport behavior inside the oil-impregnated pressboard insulation of converter transformers cannot be neglected. However, at present, current knowledge is usually derived from empirical or theoretical values, lacks experimental studies, and often ignores the effects of temperature and field strength under actual operating conditions. In this paper, based on the variable-temperature surface potential decay (SPD) method, a carrier mobility measurement platform for oil-impregnated pressboard is established, and the carrier mobility values for different combinations of oil and oil-impregnated pressboard are obtained experimentally to analyze and reveal the influence mechanisms of temperature and field strength on the carrier mobility. The results indicate the following: (1) The positive and negative carrier mobilities of oil-impregnated pressboard are in the range of 10−12–10−13 m2·V−1·s−1, and the negative carrier mobility is always higher than the positive carrier mobility. (2) The carrier mobility is positively correlated with the changes of temperature and field strength, and when the temperature increases from 20 °C to 80 °C, the positive and negative carrier mobilities increase by 4.01 times and 4.72 times, respectively; when the field strength increases from 1 kV/mm to 7 kV/mm, the positive and negative carrier mobility increases by 2.53 and 2.72 times, respectively. (3) The carrier mobility of the pressboard with a higher oil absorption rate changes more significantly with temperature; when the field strength is 7 kV/mm and the temperature increases from 20 °C to 80 °C, the positive polarity carrier mobility increases from 3.96 × 10−13 m2·V−1·s−1 to 2.64 × 10−11 m2·V−1·s−1, an increase of 66.67 times, while the increase in the carrier mobility of the pressboard with a lower oil absorption rate is only 1.59 times. (4) The carrier mobility of the naphthenic transformer oil-impregnated pressboard is higher than that of the paraffin-based transformer oil-impregnated pressboard, and the carrier mobility of two kinds of naphthenic transformer oil-impregnated pressboard is 3.16 times and 2.47 times higher than that of the paraffin-based transformer oil-impregnated pressboard, respectively, under the conditions of 60 °C and 7 kV/mm. (5) Utilizing the Darcy model and microscopic scanning results of the pressboard morphology, it was revealed that permeability and fiber structure are key factors influencing the variation in carrier mobility. The research results of this paper can provide theoretical basis for the calibration and optimization of the oil-pressboard insulation structure of converter transformers.

Relationship Between Frequency of Physical Activity, Functional Mobility, and Self-Perceived Health in People with Different Levels of Pain: A Cross-Sectional Study.

Background: Habits including regular physical activity are necessary for maintaining good health. Functional mobility, including walking and going up and down stairs, is essential for personal autonomy and well-being. Pain is a condition related to biological and psychosocial aspects that influence people's lives. Objective: The main objectives of this study were (1) to analyse the associations between physical activity frequency (PAF) and self-perceived health (SPH) and functional mobility (walking and going up and down stairs) in middle-aged and older people living in Spain with different pain levels; and (2) to analyse the risk factors for having a negative SPH and functional mobility difficulties by calculating the probabilistic risks adjusted by different variables (sex, body mass index, social class, civil status, smoking status, pain level, and PAF). Methods: A cross-sectional study based on the European Health Survey data in Spain (EHSS 2014-2020) and The Spanish National Health Survey (SNHS 2017) was carried out, with a final sample of 21,152 participants with ages between 40 and 79 years. Results: Associations between high pain levels and worse SPH and difficulties in walking and climbing stairs were found. Lower PAF levels were associated with higher-probability risks of having a negative SPH and difficulties in walking and climbing stairs. Conclusions: Physical inactivity emerged as an important risk factor for worse SPH and functional mobility. These associations underline the importance that PA programmes can play in the improvement of health and functional mobility, as well as in other aspects, in people with pain.

Impact of laterally mobile surface charge on diffusiophoresis of hydrophobic rigid colloids

The diffusiophoresis of charged hydrophobic nanoparticles (NPs) governed by an imposed ionic concentration gradient is analysed. The main objective is to elucidate the impact of the laterally mobile adsorbed surface ions at the interface on the propulsion of the hydrophobic NPs in diffusiophoresis. In addition, the dielectric polarization due to the difference in dielectric constant between the NPs and the suspension medium is also considered. The mobile surface ions create a friction as well as an electric force at the hydrophobic surface, which leads to a modification of the slip velocity condition and the slip length. We obtain an exact numerical solution of the governing electrokinetic equations in their full form by adopting a control volume formulation. The numerical model is supplemented by analytical solutions derived based on the Debye–Hückel linearization. We find that the lateral mobility of the surface ions obstruct the coions to diffuse from the higher concentration side to the lower concentration side, which results in a repulsive force to the particle leading to the occurrence of a negative mobility. Based on the numerical results and analytical solutions, we have shown that for a fully mobile surface charge, the diffusiophoresis of a hydrophobic NP is identical to the diffusiophoresis of a liquid droplet whose viscosity is related to the slip length of the hydrophobic particle. We establish that the dielectric polarization enhances the velocity of a hydrophobic particle, which has potential applications in the practical context.

Towards the Politics of Difference: Mobility and Ethnic Identity in Richard Ford’s Bascombe Novels

Mobility holds profound ethnic, class, and cultural significance in the fiction of the contemporary American writer Richard Ford. Through an analysis of his representative works, including Independence Day, The Lay of the Land and Let Me Be Frank with You, it becomes evident that Ford portrays the “negative mobility” of African Americans under spatial isolation, the transnational mobility of a Chinese immigrant, and the upward social mobility of both groups. In doing so, Ford illuminates disparities in mobility rights, routes, and friction among different ethnic groups, while also revealing shifts in their social status, values, and sense of identity. Furthermore, Ford reflects upon the social reality wherein ethnic minority groups encounter othering and marginalization upon integration into mainstream American society. This exposure lays bare the widespread systemic racial discrimination and deficiencies within the American political and economic system. Additionally, Ford’s depiction of upward social mobility among ethnic minorities underscores the effectiveness of the politics of difference as a means to resist authority and construct ethnic identity. Focusing on the mobility of ethnic minorities deepens our understanding of the survival dilemma and identity crisis faced by them.

Memory-induced absolute negative mobility

Non-Markovian systems form a broad area of physics that remains greatly unexplored despite years of intensive investigations. The spotlight is on memory as a source of effects that are absent in their Markovian counterparts. In this work, we dive into this problem and analyze a driven Brownian particle moving in a spatially periodic potential and exposed to correlated thermal noise. We show that the absolute negative mobility effect, in which the net movement of the particle is in the direction opposite to the average force acting on it, may be induced by the memory of the setup. To explain the origin of this phenomenon, we resort to the recently developed effective mass approach to dynamics of non-Markovian systems.

Diffusiophoretic Transport of Charged Colloids in Ionic Surfactant Gradients Entirely below versus Entirely above the Critical Micelle Concentration.

When placed in an ionic surfactant gradient, charged colloids will undergo diffusiophoresis at a velocity, uDP = MDP∇ ln S, where MDP is the diffusiophoretic mobility and S is the surfactant concentration. The diffusiophoretic mobility depends in part on the charges and diffusivities of the surfactants and their counterions. Since micellization decreases surfactant diffusivity and alters charge distributions in a surfactant solution, MDP of charged colloids in ionic surfactant gradients may differ significantly when surfactant concentrations are above or below the critical micelle concentration (CMC). The role of micelles in driving diffusiophoresis is unclear, and a previously published model that accounts for micellization suggests the possibility of a change in the sign of MDP above the CMC [Warren, P. B.; . Soft Matter 2019, 15, 278-288]. In the current study, microfluidic channels were used to measure the transport of negatively charged polystyrene colloids in sodium dodecyl sulfate (SDS) surfactant gradients established at SDS concentrations that are either fully above or fully below the CMC. Interpretation of diffusiophoresis was aided by measurements of the colloid electrophoretic mobility as a function of SDS concentration. A numerical transport model incorporating the prior diffusiophoretic mobility model for ionic surfactant gradients was implemented to elucidate signatures of positive and negative diffusiophoretic mobilities and compare with experiments. The theoretically predicted sign of the diffusiophoretic mobility below the CMC was determined to be particularly sensitive to uncertainty in colloid and surfactant properties, while above the CMC, the mobility was consistently predicted to be positive in the SDS concentration range considered in the experiments conducted here. In contrast, experiments only showed signatures of a negative diffusiophoretic mobility for these negatively charged colloids with no change of sign. Colloid diffusiophoretic transport measured in micellar solutions was more extensive than that below the CMC with the same ∇ ln S.

Magnetization spiral structure and high domain wall velocity induced by inertial effect

In ultrafast magnetism, i.e., the short time scales such as picosecond and femtosecond, we report that the spiral structure of magnetization can be formed by the inertial effect. Comparing with the case of fast magnetism in nanosecond time scale, we can obtain a higher velocity of domain wall in ultrafast magnetism due to the driving of inertial moment. There is a critical value τc of angular momentum relaxation time τ for the inertial breakdown in uniaxial ferromagnet. Under the action of the inertial effect the domain wall width shows the characteristics of increases firstly as τ<τc, and then decreasing as τ>τc. It directly leads to the positive or negative mobility for the domain wall velocity as the inertia is less than or exceeds the critical value, respectively. In the high frequency mode (i.e., high field mode), we obtain the limit domain wall velocity, i.e., V→1/ατ. The smaller the inertia or damping, the faster the domain wall moves. For the case of biaxial anisotropic ferromagnets, the domain wall width and velocity decreases with the increasing inertia term, respectively. In the presence of inertia effect, there is an another critical magnetic field hc. The domain wall width decreases with the increase of the magnetic field as h<hc, while increases as h>hc. However, the domain wall velocity shows a nearly linear increase with the magnetic field. These results indicate that the ultrafast magnetism has more advantages than fast magnetism. It also provides a good control technique for rapid information processing in the future.

Selective measurement of Cl2 and HCl based on dopant-assisted negative photoionization ion mobility spectrometry combined with semiconductor cooling.

This study presents an efficient approach for the precise detection of chlorine gas (Cl2) and hydrogen chloride (HCl), harmful pollutants frequently emitted from chlor-alkali and various industrial processes. These substances, even in trace amounts, pose significant health risks. Ion mobility spectrometry (IMS), known for its sensitivity in pollutant detection, traditionally struggles to differentiate between Cl2 and HCl due to the similarity of their product ions, Cl-. To overcome this limitation, we introduce a novel technique combining dopant-assisted negative photoionization ion mobility spectrometry (DANP-IMS) with an automatic semiconductor cooling system. This unique combination utilizes the differential cryogenic removal efficiencies of Cl2 and HCl to segregate these gases before analysis. By applying DANP-IMS, we achieved selective measurement of Cl- ion signal intensities under both standard and cryogenic conditions, facilitating the accurate quantification of total chlorine and Cl2 levels. We then determined HCl concentrations by deducting the Cl2 signal from the total chlorine readings. Our approach demonstrated detection limits of 2.0 parts per billion (ppb) for Cl2 and 0.8 ppb for HCl, across a linear detection range of 0-200 ppb. Moreover, our method's capability for real-time atmospheric monitoring of Cl2 and HCl near industrial sites underscores its utility for environmental monitoring, offering a robust solution for the separate and precise measurement of these pollutants.

Charge carrier transport in perylene-based and pyrene-based columnar liquid crystals.

Electron and hole transport characteristics were evaluated for perylene-based and pyrene-based compounds using electron-only and hole-only devices. The perylene presented a columnar hexagonal liquid crystal phase at room temperature with strong molecular π-stacking inside the columns. The pyrene crystallizes bellow 166 °C, preserving the close-packed columnar rectangular structure of the mesophase. Photophysical analysis and numerical calculations assisted the interpretation of positive and negative charge carrier mobilities obtained from fitting the space charge limited regime of current vs voltage curves. The pyrene-based material demonstrated an electron mobility two orders of magnitude higher than the perylene one, indicating the potential of this class of materials as electron transporting layer.

Negative Poisson's ratio and anisotropic carrier mobility in ternary Janus Si2XY (X/Y= S, Se, Te): First-principles prediction

In this Letter, the structural, mechanical, electronic, and transport properties of two-dimensional (2D) ternary Janus Si2XY (X/Y= S, Se, Te) monolayers are studied based on the calculations using first-principles density functional theory. All three structures are found as direct semiconductors with moderated bandgap energies and good stabilities for experimental synthesis. The transport properties are also examined by calculating the carrier mobilities. We find that the carrier mobilities of all three monolayers are anisotropic not only between the electrons and holes but also between the two transport directions. The Si2SSe monolayer exhibited the highest electron mobility of 897.66 cm2 V−1 s−1 in the x axis. Amazingly, our calculations reveal that the Si2XY monolayers are auxetic materials with negative Poisson's ratio along both x and y axes. Particularly, the Si2SSe has the largest negative Poisson's ratio value of –0.131 in the x direction. These obtained results open more prospects for advanced applications of these materials in electronics, optoelectronics, and nanomechanics.

Paradoxical nature of negative mobility in the weak dissipation regime.

We reinvestigate a paradigmatic model of nonequilibrium statistical physics consisting of an inertial Brownian particle in a symmetric periodic potential subjected to both a time-periodic force and a static bias. In doing so, we focus on the negative mobility phenomenon in which the average velocity of the particle is opposite to the constant force acting on it. Surprisingly, we find that in the weak dissipation regime, thermal fluctuations induce negative mobility much more frequently than it happens if dissipation is stronger. In particular, for the very first time, we report a parameter set in which thermal noise causes this effect in the nonlinear response regime. Moreover, we show that the coexistence of deterministic negative mobility and chaos is routinely encountered when approaching the overdamped limit in which chaos does not emerge rather than near the Hamiltonian regime of which chaos is one of the hallmarks. On the other hand, at non-zero temperature, the negative mobility in the weak dissipation regime is typically affected by weak ergodicity breaking. Our findings can be corroborated experimentally in a multitude of physical realizations, including, e.g., Josephson junctions and cold atoms dwelling in optical lattices.

Absolute Negative Mobility of an Active Tracer in a Crowded Environment.

Absolute negative mobility (ANM) refers to the situation where the average velocity of a driven tracer is opposite to the direction of the driving force. This effect was evidenced in different models of nonequilibrium transport in complex environments, whose description remains effective. Here, we provide a microscopic theory for this phenomenon. We show that it emerges in the model of an active tracer particle submitted to an external force and which evolves on a discrete lattice populated with mobile passive crowders. Resorting to a decoupling approximation, we compute analytically the velocity of the tracer particle as a function of the different parameters of the system and confront our results to numerical simulations. We determine the range of parameters where ANM can be observed, characterize the response of the environment to the displacement of the tracer, and clarify the mechanism underlying ANM and its relationship with negative differential mobility (another hallmark of driven systems far from the linear response).

Contribution of non-ionic interactions on bile salt sequestration by chitooligosaccharides: Potential hypocholesterolemic activity

Chitooligosaccharides have been suggested as cholesterol reducing ingredients mostly due to their ability to sequestrate bile salts. The nature of the chitooligosaccharides-bile salts binding is usually linked with the ionic interaction. However, at physiological intestinal pH range (6.4 to 7.4) and considering chitooligosaccharides pKa, they should be mostly uncharged. This highlights that other type of interaction might be of relevance. In this work, aqueous solutions of chitooligosaccharides with an average degree of polymerization of 10 and 90 % deacetylated, were characterized regarding their effect on bile salt sequestration and cholesterol accessibility. Chitooligosaccharides were shown to bind bile salts to a similar extent as the cationic resin colestipol, both decreasing cholesterol accessibility as measured by NMR at pH 7.4. A decrease in the ionic strength leads to an increase in the binding capacity of chitooligosaccharides, in agreement with the involvement of ionic interactions. However, when the pH is decreased to 6.4, the increase in charge of chitooligosaccharides is not followed by a significant increase in bile salt sequestration. This corroborates the involvement of non-ionic interactions, which was further supported by NMR chemical shift analysis and by the negative electrophoretic mobility attained for the bile salt-chitooligosaccharide aggregates at high bile salt concentrations. These results highlight that chitooligosaccharides non-ionic character is a relevant structural feature to aid in the development of hypocholesterolemic ingredients.

Effects of a small amount of H2O on negative ion mobility and ion‐molecule reactions in O2 at atmospheric pressure

AbstractIn this study, we have measured the negative ion mobility in O2 at high pressures with a little amount of H2O concentration between 15 and 17,000 ppb. After that, we carried out a Monte Carlo simulation using mobility of electrons, that of the ions obtained in the measurements, and rate coefficients of ion‐molecule reactions. As a result, the mobility value 2.39 cm2/V·s of O4¯ is obtained in ultrahigh purity O2 of which the H2O concentration is between 15 and 100 ppb. Moreover, the mobility decreases with the H2O concentrations at which the ion species are considered to be O2¯·(H2O)n (n = 1, 2, 3). Then, we compared the experimental result with that of the simulation and estimated the ion mobility and rate coefficients of ion molecule reactions. Simulation results using estimated values of the ion mobility and rate coefficients agree well with measurement results.

Auxetic and multiferroic MP5 (M = Al, Ga): a novel 2D material with negative Possion's ratio and high anisotropic carrier mobility.

In the field of materials science, the development of multifunctional 2D materials has been a long-standing research objective. In this study, we employ first-principles calculations to predict a novel 2D material named MP5 (M = Al, Ga), which exhibits ferroelasticity, ferroelectricity, negative Poisson's ratio, and high anisotropic carrier mobility. Our investigation reveals that a single layer of MP5 displays multiferroic behavior, wherein ferroelasticity and ferroelectricity are coupled. The remarkable structural anisotropy of MP5 enables easy switching between ferroelastic and ferroelectric states, rendering it suitable for nonvolatile memory applications. Simultaneously, monolayer AlP5 (GaP5) demonstrates a negative Poisson's ratio of -0.074 (-0.058) and a carrier mobility of up to 91 720 cm2 V-1 S-1 (99 690 cm2 V-1 S-1). These exceptional properties position monolayer MP5 as a highly versatile and promising 2D material for implementation in nanomechanical and microelectromechanical devices.

Protein fractionation of Hibiscus cannabinus (kenaf) seeds, its characterization, and potential use for water treatment.

This study evaluates the coagulation performance of kenaf protein fractions (KPFs) comprising of albumin (AlbKP), globulin (GloKP), prolamin (ProKP), and glutenin (GluKP), in the treatment of high (500 NTU), medium (150 NTU), and low (30 NTU) turbidity water. Based on preliminary experimental results, the study focused on GloKP due to it outperforming the other kenaf coagulation products (KCPs) in all water types tested. The influence of GloKP, both as a primary coagulant and coagulant aid to aluminum sulfate (AS) on organic matter removal, was examined. Parametric analysis on turbidity, TSS, pH, dosages, retention time, and KPFs storage time was completed. Results indicated that GloKP could be used both as a primary coagulant and coagulant aid. GloKP had a higher turbidity and solids removal than the AlbKP and other KPFs (ProKP and GluKP). Solution pH greatly influenced the performance of the GloKP, and optimum dosage at pH 2 resulted in the highest organic matter removal. High dosages also resulted in negative mobility of particles and a more stable suspension. When used as a coagulant aid to AS, GloKP was more effective in removing dissolved organic carbon (DOC). Scanning electron microscopy elemental analysis (SEM-EDAX) and Fourier transform infrared (FT-IR) spectra showed the structure of the KPFs. SEM-EDAX indicated the presence of metal cations capable of forming complexes essential for flocs formation. The enhanced floc formation, detailed in this paper, is ascribed to the collective effect of charge neutralization of the AS species and the adsorption and bridging effect of the GloKP, which improves the bonds formed between flocs. The coagulation-flocculation process can be significantly improved using dual coagulants. GloKP was also an excellent alternative to its crude (CrKP) and solvent extract (HxKP) form for removing suspended and dissolved particles from all water types. PRACTITIONER POINTS: Kenaf protein fractionates can destabilize stable particles. The globulin protein fractionate (GloKP) aggregated the most particles and contained least dissolved organic material. GloKP is pH sensitive with pH 2 reported as best working pH. Coagulant dosage and coagulation mechanism were assessed.

Roughness in the periodic potential induces absolute negative mobility in a driven Brownian ratchet.

Absolute negative mobility, where particles move opposite to the direction as governed by the external load, is an anomalous transport property of a Brownian ratchet and has technological implications in mass separation and bioanalytical applications. We numerically investigated here the effect of roughness in symmetric periodic potential on the negative mobility of a driven inertial Brownian ratchet in the presence of an external load. We show that the microscopic spatial heterogeneity of the potential can generate negative mobility which would not otherwise be possible under smooth potential in the concerned parameter space. We determined the optimal condition in terms of parameter space for such anomalous behavior. Our calculations indicate that the shift of balance towards the negative velocity phase in the temporal oscillations of velocity and weakly chaotic dynamics are responsible factors for roughness-induced negative mobility. These calculations highlight a constructive role of roughness in the anomalous transport properties of Brownian ratchet.

Distribution, dis-sumption and dis-appointment: The negative geographies of city logistics

Critical approaches to logistics, in dialogue with geography and related disciplines, have exposed the turbulence behind apparently seamless transnational circulations of stuff. As everyday urban life becomes increasingly structured through logistical practices and expectations which imbricate consumption and distribution, now is an appropriate moment to take stock of these dialogues. Reviewing them, the article identifies three spatial assumptions – peripheral geographies, seamless consumption, forward motion – proposing that they express an additive, forward-leaning representation of logistics. In response, it draws upon debates on ‘negativity’ to suggest geographers pay greater attention to logistics’ negative spaces (voids), affects (dis-appointments) and mobilities (reversals).

Anomalous transport tuned through stochastic resetting in the rugged energy landscape of a chaotic system with roughness.

Stochastic resetting causes kinetic phase transitions, whereas its underlying physical mechanism remains to be elucidated. We here investigate the anomalous transport of a particle moving in a chaotic system with a stochastic resetting and a rough potential and focus on how the stochastic resetting, roughness, and nonequilibrium noise affect the transports of the particle. We uncover the physical mechanism for stochastic resetting resulting in the anomalous transport in a nonlinear chaotic system: The particle is reset to a new basin of attraction which may be different from the initial basin of attraction from the view of dynamics. From the view of the energy landscape, the particle is reset to a new energy state of the energy landscape which may be different from the initial energy state. This resetting can lead to a kinetic phase transition between no transport and a finite net transport or between negative mobility and positive mobility. The roughness and noise also lead to the transition. Based on the mechanism, the transport of the particle can be tuned by these parameters. For example, the combination of the stochastic resetting, roughness, and noise can enhance the transport and tune negative mobility, the enhanced stability of the system, and the resonant-like activity. We analyze these results through variances (e.g., mean-squared velocity, etc.) and correlation functions (i.e., velocity autocorrelation function, position-velocity correlation function, etc.). Our results can be extensively applied in the biology, physics, and chemistry, even social system.

Direction reversal of non-Hermitian skin effect via coherent coupling

Absolute negative mobility (ANM) in nonequilibrium systems depicts the possibility of particles propagating toward the opposite direction of an external force. We uncover in this work a phenomenon analogous to ANM regarding eigenstate localization and particle transport in non-Hermitian systems under the influence of the non-Hermitian skin effect (NHSE). A coherent coupling between two non-Hermitian chains individually possessing the same preferred direction of NHSE is shown to cause a direction reversal of NHSE for all eigenmodes. This concept is further investigated in terms of time evolution dynamics using a non-Hermitian quantum walk platform within reach of current experiments. Our findings are explained both qualitatively and quantitatively. The possible direction reversal of NHSE can potentially lead to interesting applications.