Interaction Forces Research Articles

Coupled CFD-DEM modeling of surface erosion in granular soils: Simulation of erosion function apparatus experiments

This study introduces a numerical modeling approach that couples the computational fluid dynamics (CFD) with the discrete element method (DEM) to simulate grain-scale soil erosion processes induced by water flows. In this modeling framework, CFD simulates fluid flows by solving the volume-averaged Navier-Stokes equations, and uses the k-ω turbulent model for turbulent flows. Simultaneously, DEM computes the displacement of solid particles by incorporating the fluid-particle interactions driven by fluid flows while adhering to Newton's laws of motion. These interactions encompass drag force, buoyancy force, pressure-gradient force, and viscous force exerted by fluid flows and acting on the particles. The coupled CFD-DEM modeling adeptly replicates soil erosion processes, demonstrating good alignment with results obtained from laboratory erosion function apparatus (EFA) tests. In particular, the DEM facilitates the estimation of shear stress acting on the soil surface based on fluid-particle interaction forces, which has been roughly approximated by empirical or semi-empirical models. This study underscores the capability of coupled CFD-DEM in providing valuable insights into the grain-scale behavior of soil particles subjected to fluid flows, with the potential for extension to address soil erosion and fines migration.

In-situ growth of Fe-MOF on magnetic materials by self-template method to enhance practicality and removal of tetracycline antibiotics from aqueous solution

In this work, core–shell structured Fe3O4@PCN-333 (Fe) composite was constructed using a self-template method, in which Fe3O4 microspheres not only serve as magnetic centers but also provide Fe (III) for the preparation of PCN-333 (Fe). PCN-333 (Fe) uniformly grew as a shell on the surfaces of the microspheres, and the shell thickness was approximately 38 nm. The composite exhibited high adsorption performance, with maximum adsorption capacities of 471.7, 303.3 and 314.5 mg/g for chlortetracycline, tetracycline and oxytetracycline, respectively. The adsorption of tetracycline antibiotics (TCs) was based on the Langmuir and pseudo-second-order model, and external diffusion and pore diffusion were the rate-limiting steps in adsorption. The strong adsorption capacity was attributed to the mechanism of π–π interaction, coordination bonds, electrostatic interaction, hydrogen bonding, and van der Waals force. Fe3O4@PCN-333 (Fe) composite displayed good stability in the aqueous solution, strong TCs adsorption capacity, high selectivity, anti-interference performance for adsorbing TCs, fast recovery with external magnetic field, reusability, thus effectively reducing the cost for removing water pollutants. These features make the composite a potential material for removing TCs in the environment.

Dynamics of converting skyrmion bags with different topological degrees into skyrmions in synthetic antiferromagnetic nanotracks

Skyrmion bags are spin textures with any integer topological degree, which can be driven by spin-polarized currents and generate multiple skyrmions when passing through racetracks with special geometries. We have proposed three nanotrack configurations with different narrow channels on synthetic antiferromagnetic racetracks and investigated the dynamic process of current-induced conversion of skyrmion bags into skyrmions. We have found that when skyrmion bags enter narrow channels, they can be converted into magnetic domains, while when the driving force from spin-transfer torque is strong enough, the magnetic domains can break free from the pinning at the ends of channels and form skyrmions. Both the number of channels and driving current density affect the number of generated skyrmions. As the number of channels rises, magnetic domains split at the junctions of channels, forming more magnetic domains and producing more skyrmions. Furthermore, the number of generated skyrmions is also related to the quantity, arrangement, and interaction forces of inner antiskyrmions. When the number of channels remains constant, the number of antiskyrmions only affects the transition of skyrmion bags to magnetic domains and does not affect the movement of magnetic domains or the transition of magnetic domains to skyrmions. The maximum of generated skyrmions in nanotracks with triple channels reaches 9. Dzyaloshinskii–Moriya interaction and anisotropy may play an important role in the structural stability of skyrmion bags, which can affect the splitting behavior of skyrmion bags. This work is beneficial for the design of artificial synapses and the application of neuromorphic computing based on skyrmion bags.

Comparative Evaluation of Interaction Force Characteristics for the Lipopolysaccharide of Yersinia pseudotuberculosis and Antibodies by Optical Trapping and Atomic Force Microscopy

Optical tweezers and atomic force microscopy were used for comparative evaluation of the interaction force between the lipopolysaccharide of Yersinia pseudotuberculosis and monoclonal antibodies. This paper discusses the peculiarities of two methods which allow determining significant differences in the values of the measured force required to rupture the interaction of probe sensitized by lipopolysaccharide (polystyrene microsphere for optical tweezers and silicon nitride cantilever for atomic force microscopy) with substrate (glass and mica, respectively) covered with monoclonal antibodies. In atomic force microscopy, the cantilever slides along the substrate for some time after the piezo stage is brought to a stop, causing changes in the spatial structure of sensitins and, therefore, redistribution of multiple bonds between the lipopolysaccharide agglomerate and antibodies. No significant displacement of the microsphere along the substrate occurs when an optical tweezers setup is used, and, unlike atomic force microscopy, the breaking of a complex bond between lipopolysaccharide and complementary antibodies is recorded in the form of a single and short-term (1–2 ms) leap of the photodetector signal employing optical tweezers. The recorded values of the force required to rupture the interaction measured by both methods are relative and vary depending on the chosen experimental conditions. It is shown that the non-specific component of the force needed to break the interaction measured by atomic force microscopy is significantly higher than that determined with optical tweezers.

Dynamic response of pile–slab retaining wall structure under rockfall impact

Abstract. Pile–slab retaining walls, as innovative rockfall protection structures, have been extensively utilized in the western mountainous regions of China. With their characteristics of a small footprint, high interception height, and ease of construction, these structures demonstrate promising potential for application in mountainous regions worldwide, such as the Himalayas, Andes, and Alps. However, their dynamic response upon impact and impact resistance energy remain ambiguous due to the intricate composite nature of the structures. To elucidate this, an exhaustive dynamic analysis of a four-span pile–slab retaining wall with a cantilever section of 6 m under various impact scenarios was conducted utilizing the finite-element numerical simulation method. The rationality of the selected material constitutive models and the numerical algorithm was validated by reproducing two physical model tests. The simulation results reveal the following. (1) The lateral displacement of the pile at the ground surface and the concrete damage under the pile at the impact center are greater than those under the slab at the impact center, implying that the impact location has a significant influence on the stability of the structure. (2) There is a positive correlation between the response indexes (impact force, interaction force, lateral deformation of pile and slab, concrete damage) and the impact velocities. (3) The rockfall peak impact force, the ratio of the peak impact force to the peak interaction force, and lateral displacement of the pile at the ground surface had strong linear relationships with rockfall energy. (4) Relative to the bending moment, shear force, and damage degree, the lateral displacement of the pile at the ground surface is the first to reach its limit value. Taking the lateral displacement of the pile at the ground surface as the controlling factor, the estimated maximum impact energy that the pile–slab retaining wall can withstand is 905 kJ in this study when the structure top is taken as the impact point. In cases where the impact energy of falling rocks exceeds 905 kJ, it is recommended to optimize the mechanical properties of the cushion layer, improve the elastic modulus of concrete, increase the reinforcement ratio of longitudinal tension bars, enlarge the section size of piles at ground level, or add anchoring measures to enhance the bending resistance of the retaining structure.

Human-Centered Coordination for Robot-Assisted Equipment Transport

Abstract This work explores how to use an unmanned ground vehicle (UGV) to offload the physical burdens of equipment from humans. This work formulates Dynamic Alignment Following and compares it to Position-Based Following techniques. We describe the control strategies of both following methods and implement them in a dynamic simulation and a physical prototype. We test the performance of the two following methods and show that Dynamic Alignment Following can reduce robot positional error and interaction force between the human and the robot. We then analyze the energetics and the performance of the human-UGV team for candidate transportation tasks. The presence of the robot can make some tasks take longer to perform. Nonetheless, the results show that for the candidate tasks, the robot can reduce human average metabolic power and average overall task energy.

Changes in Texture and Collagen Properties of Pork Skin during Salt-Enzyme-Alkali Tenderization Treatment.

The effects of salt-enzyme-alkali progressive tenderization treatments on porcine cortical conformation and collagen properties were investigated, and their effectiveness and mechanisms were analyzed. The tenderization treatment comprised three treatment stages: CaCl2 (25 °C/0-30 min), papain (35 °C/30-78 min), and Na2CO3 (25 °C/78-120 min). The textural, microscopic, and collagenous properties (content, solubility, and structure) of pork skin were determined at the 0th, 30th, 60th, 90th, and 120th min of the treatment process. The results showed that the shear force, hardness, and chewability of the skin decreased significantly (p < 0.05), and the elasticity exhibited a gradual increase with the progression of tenderization. The content and solubility of collagen showed no significant change at the CaCl2 treatment stage. However, the soluble collagen content increased, the insoluble collagen content decreased, and the collagen solubility increased by 18.04% during the subsequent treatment with papain and Na2CO3. Meanwhile, the scanning electron microscopy results revealed that the regular, wavy structure of the pig skin collagen fibers gradually disappeared during the CaCl2 treatment stage, the overall structure revealed expansion, and the surface microscopic pores gradually increased during the papain and Na2CO3 treatment stages. The findings of the Fourier transform infrared spectroscopy analysis indicated that the hydrogen bonding interactions between the collagen molecules and the C=O, N-H and C-N bonds in the subunit structure of collagen were substantially altered during treatment and that the breakage of amino acid chains and reduction in structural ordering became more pronounced with prolonged treatment. In the tertiary structure, the maximum emission wavelength was blue-shifted and then red-shifted, and the fluorescence intensity was gradually weakened. The surface hydrophobicity was slowly increased. The salt-enzyme-alkali tenderization treatment considerably improved the physical properties and texture of edible pork skins by dissolving collagen fibers and destroying the structure of collagen and its interaction force.

A greedy assist-as-needed controller for end-effect upper limb rehabilitation robot based on 3-DOF potential field constraints.

It has been proven that robot-assisted rehabilitation training can effectively promote the recovery of upper-limb motor function in post-stroke patients. Increasing patients' active participation by providing assist-as-needed (AAN) control strategies is key to the effectiveness of robot-assisted rehabilitation training. In this paper, a greedy assist-as-needed (GAAN) controller based on radial basis function (RBF) network combined with 3 degrees of freedom (3-DOF) potential constraints was proposed to provide AAN interactive forces of an end-effect upper limb rehabilitation robot. The proposed 3-DOF potential fields were adopted to constrain the tangential motions of three kinds of typical target trajectories (one-dimensional (1D) lines, two-dimensional (2D) curves and three-dimensional (3D) spirals) while the GAAN controller was designed to estimate the motor capability of a subject and provide appropriate robot-assisted forces. The co-simulation (Adams-Matlab/Simulink) experiments and behavioral experiments on 10 healthy volunteers were conducted to validate the utility of the GAAN controller. The experimental results demonstrated that the GAAN controller combined with 3-DOF potential field constraints enabled the subjects to actively participate in kinds of tracking tasks while keeping acceptable tracking accuracies. 3D spirals could be better in stimulating subjects' active participation when compared to 1D and 2D target trajectories. The current GAAN controller has the potential to be applied to existing commercial upper limb rehabilitation robots.

Photo-Triggered Fluorescence Polyelectrolyte Nanoassemblies: Manipulate and Boost Singlet Oxygen in Photodynamic Therapy.

Photodynamic therapy (PDT) is a clinically approved therapeutic modality that has shown great potential for cancer treatment. However, there exist two major problems hindering PDT applications: the nonspecific phototoxicity requiring patients to stay in dark post-PDT, and the limited photodynamic efficiency. Herein, we report a photo-triggered porphyrin polyelectrolyte nanoassembling (photo-triggered PPN) strategy, in which porphyrin photosensitizer and photoswitchable energy accepter are assembled into polyelectrolyte micelles by a combined force of charge interaction and metal-ligand coordination. The polyelectrolyte-based PPN exhibits good biocompatibility, and bestows a unique "confining isolated" inner microenvironment for fully overcoming the π-π stacking of porphyrins with significant photodynamic efficiency (123-fold enhancement). Due to the high Förster resonance energy transfer (FRET) (91.5%) between porphyrin and photoswitch in closed-form, we could use light as a specific trigger to modulate photoswitch between closed- and open-form, and manipulate the 1O2 generation in three stages: pre-PDT (quenching 1O2 generation), during PDT (activating 1O2 generation), and post-PDT (silencing 1O2 generation). This de novo strategy has for the first time realized remotely manipulating and boosting 1O2 generation in PDT, well resolving the critical and general challenges of limited photodynamic efficiency and side effects from nonspecific phototoxicity.

Core-shell MIL-53(Al)–NH2@UiO-66 coated solid-phase microextraction Arrow for the selective enrichment of nine alkylphenols in milk

Metal-organic frameworks (MOFs) hold significant potential for sample preparation, but single-MOF materials often face limitations in selectivity and extraction efficiency. To overcome these, a mesoporous MIL-53(Al)–NH2@UiO-66 composites with a core–shell structure was synthesized using an epitaxial growth strategy. This composite leverages the complementary properties of both MOFs, offering enhanced active sites and interaction forces for analytes. The structure and integration of the composite were characterized using Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction, confirming their successful integration. To address the challenge of detecting alkylphenols (APs) in food matrices, known for their endocrine-disrupting properties and low concentrations, a new solid-phase microextraction (SPME) Arrow was fabricated using the MIL-53(Al)–NH2@UiO-66 composite combined with polyacrylonitrile as a binder. APs were detected using ultra-performance liquid chromatography and quadrupole time-of-flight tandem mass spectrometry (UPLC-ESI-Q-ToF/MS). The developed SPME Arrow-UPLC-ESI-Q-ToF/MS method exhibits good linearity (R2 ≥ 0.9958), wide linear range (0.01–1000 μg L–1), and high sensitivity (limits of detection ranging from 0.005 to 0.01 μg L–1) for APs determination. This method was validated for determining nine APs in milk samples from various packing materials, with spiked recoveries ranging from 85.2 % to 115 % and relative standard deviations from 3.4 % to 13.6 %. This study demonstrates the potential of MOF-on-MOF composites in enhancing the performance of adsorbents for SPME pretreatment, offering a promising approach for improving analytical methodologies in food safety.

A cationic polyelectrolyte for enhancing dewatering of montmorillonite-containing coal slime: adsorption and modification mechanism

ABSTRACT In this study, a cationic polyelectrolyte (Poly dimethyl diallyl ammonium chloride, PDADMAC) was introduced as a filter aid to enhance the dewatering effect of montmorillonite (MT)-containing coal slime, and compared with cationic polyacrylamide (CPAM). The dewatering performance of PDADMAC and CPAM was evaluated based on vacuum filtration experiments. The modification mechanism of PDADMAC on Mt particle surface was revealed by filter cake pore distribution, zeta potential, contact angle and Atomic Force Microscopy (AFM). The adsorption difference between PDADMAC and CPAM on Mt surface was studied by Density Functional Theory (DFT). In addition, DLVO theory further explains the mechanism of PDADMAC enhancing dewatering from the perspective of interaction force. The optimal dosage of PDADMAC was 125 g/t, and the filter cake moisture content was reduced by 3%. Compared to CPAM, PDADMAC achieves efficient dewatering at a lower dosage. PDADMAC has a more prominent ability to neutralize charge, and its effect on interparticle interactions was a potential mechanism to promote dehydration.

Regulating Intermolecular Hydrogen Bonds in Organic Cathode Materials to Realize Ultra‐stable, Flexible and Low‐temperature Aqueous Zinc‐organic Batteries

Rational design of molecular structures is one of the effective strategies to obtain high‐performance organic cathode materials. However, besides the optimization of single‐molecule structures, the influence of the "weak" interaction forces (e.g. hydrogen bonds) in organic cathode materials on the performance of batteries should be fully considered. Herein, three organic small molecules with different numbers of hydroxyl groups (namely nitrogen heterocyclic tetraketone (DAB), monohydroxyl nitrogen heterocyclic dione (HDA), dihydroxyl nitrogen heterocyclic dione (DHT)) were selected as the cathodes of aqueous zinc ion batteries (AZIBs), and the effect of the intermolecular hydrogen bonds on their electrochemical performance was studied for the first time. Clearly, the stable hydrogen‐bond networks built through the hydroxyl groups significantly enhance the cycle stability of organic small‐molecule cathodes and facilitate rapid proton conduction between the hydrogen‐bond networks through the Grotthuss mechanism, thereby endowing them with excellent rate performance. In addition, a larger and more dense two‐dimensional hydrogen‐bond network can be constructed through multiple hydroxyl groups, further enhancing the structural stability of organic small‐molecule cathodes, giving them better cycle tolerance, excellent rate performance, and extreme environmental tolerance.

Regulating Intermolecular Hydrogen Bonds in Organic Cathode Materials to Realize Ultra-stable, Flexible and Low-temperature Aqueous Zinc-organic Batteries.

Rational design of molecular structures is one of the effective strategies to obtain high-performance organic cathode materials. However, besides the optimization of single-molecule structures, the influence of the "weak" interaction forces (e.g. hydrogen bonds) in organic cathode materials on the performance of batteries should be fully considered. Herein, three organic small molecules with different numbers of hydroxyl groups (namely nitrogen heterocyclic tetraketone (DAB), monohydroxyl nitrogen heterocyclic dione (HDA), dihydroxyl nitrogen heterocyclic dione (DHT)) were selected as the cathodes of aqueous zinc ion batteries (AZIBs), and the effect of the intermolecular hydrogen bonds on their electrochemical performance was studied for the first time. Clearly, the stable hydrogen-bond networks built through the hydroxyl groups significantly enhance the cycle stability of organic small-molecule cathodes and facilitate rapid proton conduction between the hydrogen-bond networks through the Grotthuss mechanism, thereby endowing them with excellent rate performance. In addition, a larger and more dense two-dimensional hydrogen-bond network can be constructed through multiple hydroxyl groups, further enhancing the structural stability of organic small-molecule cathodes, giving them better cycle tolerance, excellent rate performance, and extreme environmental tolerance.

Semi-transparent boundary in Lee–Wick electrodynamics

In this paper, we investigate certain aspects of Lee–Wick electrodynamics near a semitransparent planar mirror. Specifically, we derive the modified propagator for the Lee–Wick gauge field in the presence of the mirror and conduct a detailed analysis of the interaction energy and the interaction force that arise between the mirror and a stationary point-like charge. We demonstrate that there are several peculiarities in this interaction compared to the results obtained for Maxwell electrodynamics. Our focus is on the divergences mitigated by the Podolsky mass term.

Statement of retraction: Bending performance of a multi-phase initially stressed plate considering interaction force

Statement of retraction: Bending performance of a multi-phase initially stressed plate considering interaction force

Tunable Coassembly of Octaarginine with Thiazolyl Benzenesulfonamides Exerts Variable Antibacterial Activity.

The cationic peptide octaarginine (R8) is a prominent cell-penetrating peptide and has been extensively researched as a carrier of diverse cell-destined cargo. In this work, we describe the coassembly of R8 with small molecule thiazolyl benzenesulfonamide (TBS) derivatives. Physical complexation of R8 with three TBS derivatives across a range of weight ratios results in the formation of a distinctive set of nano- and microstructures. A detailed structural characterization of the R8:TBS-derivative coassemblies has been performed by a combination of FTIR, XRD, SEM, and DSC. The major functional groups that facilitate coassembly include sulfonamide SO2 and NH groups of the TBS derivatives, and the guanidinium of R8, via a combination of cation-π and hydrogen-bonding interactions. The R8:4F-TBS coassembly displays singular topological features compared to R8:4Br-TBS and R8:4CH3-TBS complexes. These differences are attributed to the changes in the preferred orientation of the guanidino groups of R8 with respect to the π-surface of TBS derivatives. The modulation of forces of interaction across the R8:TBS-derivative coassemblies aligns with their respective thermal stabilities. The single-crystal structure of bare 4F-TBS has been subjected to Hirshfeld and 2D fingerprinting analysis and indicates notable variations from the crystal packing of the R8:4F-TBS coassembly. The structural differences among the R8:TBS-derivative coassemblies correlate with distinctive profiles of antibacterial activity in each case. The coassembled structures exert a variable extent of bacterial membrane disruption and damage based on the unique disposition of R8 and the potency of small molecule in each case. The aqueous suspension of R8:4F-TBS displays significant outer membrane disruption and bacterial killing compared with the other complexes. This work successfully demonstrates the hitherto unreported potential for coassembly of cell-penetrating peptides with other entities. The coassembly of R8 with small molecules highlights an attractive strategy for tuning the functional properties of each component.

Gait self-learning control based on reference trajectory generation online for an asymmetric limb rehabilitation exoskeleton

Lower limb exoskeleton (LEX) are widely used to assist stoke survivors with walking dysfunction, which is lack of a more flexible trajectory and fails to address the control challenge posed by gait variability and asymmetry in rehabilitation training. This paper introduces an asymmetric self-learning lower exoskeleton (AS-LEX) based on reference trajectory generation for the affected side. Motor intent of the unaffected limb based on thresholds was identified to classify the gait phase of stance and swing. A parameterized gait trajectory was generated online, namely a combination of circular trajectory in the stance phase and an elliptical trajectory in the swing phase. Gait self-learning control is presented to make the affected limb adaptively learn the gait parameters generated by the unaffected limb. Feasibility of the AS-LEX is demonstrated experimentally using three healthy subjects. Resuls demonstrate that overground walking in a more natural speed (with a stride length 600 mm and 700 mm) make subjects more actively learn gait of the affected side from the unaffected side. Additionally, experiments of the fatigue level of the affected limb and human-robot interaction torques were carried out, and the results indicate a more natural gait and reduced interaction forces with the AS-LEX.

Identification of fenfluramine adulteration in slimming foods using a highly sensitive immunoassay

Fenfluramine, an appetite suppressant used for weight loss, can cause significant harm if overdosed. The unauthorized addition of fenfluramine to slimming foods has raised concerns. Currently, no rapid screening method is available for the quick detection of fenfluramine in the field. This study proposes six new haptens with varying spacer arm lengths and hydrophobicity, promising to elicit antibodies capable of being highly specific and strongly binding to fenfluramine. The study found that highly hydrophobic haptens with long spacer arms favored the generation of highly sensitive antibodies. Key interaction forces for antibody recognition of fenfluramine were revealed by intrinsic molecular mechanisms. Based on the above results, monoclonal antibody for fenfluramine was prepared and an ultrasensitive icELISA method with heterologous coating strategies was developed in slimming foods. The IC50 of the method was 6.25 ng/mL, the linear detection range was 0.47–83.51 ng/mL and the detection limit was 0.10 ng/mL. Recovery rates in tea bags, tablets, capsules, coffee, and beverages ranged from 96.56 % to 108.90 %. The method was successfully applied to blind samples, showing strong correlation with HPLC-MS/MS results. Thus, the developed method is suitable for identifying fenfluramine adulteration in slimming foods.

Theoretical study of the deuteron + deuteron radiative capture

In the present work, the d + d radiative capture process is studied. This process is of significant interest for astrophysical applications. The theoretical framework of the study is based on the microscopic cluster approach in the oscillator representation. The total and partial cross sections for the reaction in terms of the astrophysical S factor are calculated. A good agreement with experimental data is achieved. The tensor force of the nuclear interaction is shown to play a key role in describing the low-energy dependence of the total cross section (astrophysical S factor).

A model-based approach for joint estimation of track irregularities and track support modulus from trackside measurements in railway turnouts

ABSTRACT The paper proposes a model-based approach for the concomitant estimation of track modulus, track irregularity, and dynamic loading by combining an analytical model of a beam on an elastic foundation with vibration data collected by a trackside measurement system. The model is empirically extended to incorporate the effects of dynamic wheel/rail interaction forces when both short wavelength defects (in the rail surface) and medium-long wavelength track irregularities (e.g. hanging sleepers, differential ballast settlement) are present. The power spectral density of the rail vertical acceleration is then exploited in combination with the extended model to estimate track parameters using least squares. The proposed method is validated on vibration data collected in a turnout of the Danish railway infrastructure over a period of 2.5 years. The obtained results show that changes over time in track modulus and track irregularities, and consequently in dynamic wheel/rail contact forces, can be efficiently monitored from trackside measurements.