Orientational Freedom Research Articles

Position and reduced attitude trajectory tracking control of quadrotors: Theory and experiments

Multirotor aerial vehicles are versatile flying robots that perform hovering, vertical take-off and landing, and aggressive maneuvers in a 3D environment. Due to their underactuated nature, the aerial vehicles' position and orientation cannot be controlled independently. For this reason, most of the quadrotors' tasks involved position tracking or regulation tasks. This paper focuses on the position-tracking problem of quadrotors using the reduced orientation of the vehicle, meaning that only two degrees of freedom of the robot's orientation are controlled. We propose an almost global exponential reduced attitude control law that aligns the aerial robot's thrust direction with the desired force that drives the robot along the desired position trajectory. For the translational subsystem, we propose a dynamic control law that drives the position and velocity of the quadrotors asymptotically to the desired trajectories. The proposed attitude control law is computationally simple, and thus, it is suitable to run on board. Finally, we provide experimental results performed on a low-cost quadrotor and a comparison study with a full-attitude controller to illustrate the performance and advantages of the proposed control laws.

Marine Fouling Release Performance of Amphiphilic Carboxybetaine Perfluoropolyether Methacrylate Polymer Coatings

AbstractAmphiphilic polymer systems have been demonstrated to be an effective and environmentally friendly approach to combat the challenges of biofouling, especially in the real ocean environment. A variety of polymer compositions containing fluorophilic perfluoropolyether (PFPE) urethane dimethacrylate and zwitterionic carboxybetaine methacrylate (CBMA) are in situ copolymerized across a broad concentration range and anchored to chemically functionalized substrates by grafting‐through polymerization. Dynamic accumulation assays with the marine diatom Navicula perminuta and the marine bacterium Cobetia marina revealed an enhanced antifouling performance in most of the amphiphilic polymer mixtures when zwitterionic units are combined with hydrophobic PFPE compounds. It is noticed that the resulting polymer networks still possess enough orientational freedom to quickly rearrange in the presence of water. It is further observed that several of the very hydrophilic formulations and some of the moderately hydrophobic formulations exhibit low fouling against the marine fouling organisms Navicula perminuta and Cobetia marina. This correlated with increased surface roughness and the ability for underwater rearrangement. Furthermore, it is discussed whether the probability that highly hydrated hydrogels, which appear sponge‐like, may create a diffuse interphase which promotes the incorporation of silt. Latter is counteracted by the hydrophobic PFPE building blocks in the amphiphilic coatings.

Sequential Dual Alignments Introduce Synergistic Effect on Hexagonal Boron Nitride Platelets for Superior Thermal Performance.

Planarly aligning 2D platelets is challenging due to their additional orientational freedom compared to 1D materials. This study reports a sequential dual-alignment approach, employing an extrusion-printing-induced shear force and rotating-magnetic-field-induced force couple for platelet planarly alignment in a yield-stress support bath. It is hypothesized that the partial alignment induced by a directional shear force facilitates subsequent axial rotation of the platelets for planar alignment under an external force couple, resulting in a synergistic alignment effect. This sequential dual-alignment approach achieves better planar alignment of 2D modified hexagonal boron nitride (mhBN). Specifically, the thermal conductivity of the 40 wt% mhBN/epoxy composite is significantly higher (692%) than that of unaligned composites, surpassing the cumulative effect of individual methods (only 133%) with a 5 times more synergistic effect. For 30, 40, and 50 wt% mhBN composites, the thermal conductivity values (5.9, 9.5, and 13.8W m-1 K-1) show considerable improvement compared to the previously reported highest values (5.3, 6.6, and 8.6W m-1 K-1). Additionally, a 3D mhBN/epoxy heat sink is printed and evaluated to demonstrate the feasibility of device fabrication. The approach enables the planar alignment of electrically or thermally conducting 2D fillers during 3D fabrication.

Molecular-Scale Investigations Reveal the Effect of Natural Polyphenols on BAX/Bcl-2 Interactions.

Apoptosis signaling controls the cell cycle through the protein-protein interactions (PPIs) of its major B-cell lymphoma 2-associated x protein (BAX) and B-cell lymphoma 2 protein (Bcl-2). Due to the antagonistic function of both proteins, apoptosis depends on a properly tuned balance of the kinetics of BAX and Bcl-2 activities. The utilization of natural polyphenols to regulate the binding process of PPIs is feasible. However, the mechanism of this modulation has not been studied in detail. Here, we utilized atomic force microscopy (AFM) to evaluate the effects of polyphenols (kaempferol, quercetin, dihydromyricetin, baicalin, curcumin, rutin, epigallocatechin gallate, and gossypol) on the BAX/Bcl-2 binding mechanism. We demonstrated at the molecular scale that polyphenols quantitatively affect the interaction forces, kinetics, thermodynamics, and structural properties of BAX/Bcl-2 complex formation. We observed that rutin, epigallocatechin gallate, and baicalin reduced the binding affinity of BAX/Bcl-2 by an order of magnitude. Combined with surface free energy and molecular docking, the results revealed that polyphenols are driven by multiple forces that affect the orientation freedom of PPIs, with hydrogen bonding, hydrophobic interactions, and van der Waals forces being the major contributors. Overall, our work provides valuable insights into how molecules tune PPIs to modulate their function.

Organization of Carotenoid Aggregates in Membranes Studied Selectively using Resonance Raman Optical Activity.

In living organisms, carotenoids are incorporated in biomembranes, remarkably modulating their mechanical characteristics, fluidity, and permeability. Significant resonance enhancement of Raman optical activity (ROA) signals of carotenoid chiral aggregates makes resonance ROA (RROA), a highly selective tool to study exclusively carotenoid assemblies in model membranes. Hence, RROA is combined with electronic circular dichroism (ECD), dynamic light scattering (DLS), molecular dynamics, and quantum-chemical calculations to shed new light on the carotenoid aggregation in dipalmitoylphosphatidylcholine (DPPC) liposomes. Using representative members of the carotenoid family: apolar α-carotene and more polar fucoxanthin and zeaxanthin, the authors demonstrate that the stability of carotenoid aggregates is directly linked with their orientation in membranes and the monomer structures inside the assemblies. In particular, polyene chain distortion of α-carotene molecules is an important feature of J-aggregates that show increased orientational freedom and stability inside liposomes compared to H-assemblies of more polar xanthophylls. In light of these results, RROA emerges as a new tool to study active compounds and drugs embedded in membranes.

Structural insights into the modulation of coronavirus spike tilting and infectivity by hinge glycans

Coronavirus spike glycoproteins presented on the virion surface mediate receptor binding, and membrane fusion during virus entry and constitute the primary target for vaccine and drug development. How the structure dynamics of the full-length spikes incorporated in viral lipid envelope correlates with the virus infectivity remains poorly understood. Here we present structures and distributions of native spike conformations on vitrified human coronavirus NL63 (HCoV-NL63) virions without chemical fixation by cryogenic electron tomography (cryoET) and subtomogram averaging, along with site-specific glycan composition and occupancy determined by mass spectrometry. The higher oligomannose glycan shield on HCoV-NL63 spikes than on SARS-CoV-2 spikes correlates with stronger immune evasion of HCoV-NL63. Incorporation of cryoET-derived native spike conformations into all-atom molecular dynamic simulations elucidate the conformational landscape of the glycosylated, full-length spike that reveals a role of hinge glycans in modulating spike bending. We show that glycosylation at N1242 at the upper portion of the stalk is responsible for the extensive orientational freedom of the spike crown. Subsequent infectivity assays implicated involvement of N1242-glyan in virus entry. Our results suggest a potential therapeutic target site for HCoV-NL63.

Magneto-Orientated Graphite Double-Layer Homo-Structure with Broadband Microwave Absorption

We utilized magnetic fields as an efficient tool to manipulate the orientation and electromagnetic properties of graphite micro-flakes (GMFs). As a result, we successfully developed a GMF double-layer homo-structure, which shows excellent electromagnetic absorption properties. By tuning the direction of a small magnetic field (850 G), vertical and horizontal aligned GMFs are produced. Their electromagnetic parameters are effectively tailored by this magneto-orientation effect, and the vertical and horizontal aligned GMFs achieve good results in terms of impedance matching and microwave absorption. With the combination of these two magneto-orientated layers, vertically oriented as the surficial impedance matching layer and horizontally oriented as the inner loss layer, we design a GMF-based double-layer homo-structure. After thickness optimization, −38.2 dB minimum reflection loss and 6.4 GHz (11.6–18.0 GHz) absorption bandwidth are achieved. Our findings further emphasize the importance of material orientation freedom and provide a magneto-strategy to design multiple-layer structures and to produce high-performance microwave devices.

Influence of orientational disorder in the adsorbent on the structure and dynamics of the adsorbate: MD simulations of SO2 in ZSM-22

Structural and dynamical behavior of SO2 molecules within ZSM-22 is studied using molecular dynamics simulations, to understand the influence of orientational disorder (OD) and inter – crystalline spacing in ZSM-22 as a function of adsorbate loading. Addition of inter-crystalline space provides connectivity of isolated pores in ZSM-22 and is shown to suppress both translational and rotational motion of SO2. We infer that geometry and dimensionality of the connecting space are important factors in determining the effects of pore connectivity on the adsorbed species behavior. As a function of OD, decrease in self-diffusion coefficient of SO2 in ZSM-22 is observed. An increase in rotational correlation time and a decrease in libration angle with OD is observed, ascribed to the restriction imposed on the orientational freedom of the adsorbate by an increase in OD. The behavior of SO2 results from an interplay of guest-host interactions and the dimensionality and geometry of confinement.

Non‐Planar Multiprocess Additive Manufacturing of Multifunctional Composites

AbstractMultiprocess additive manufacturing (AM) consists of integrating different 3D printing techniques to enable the fabrication of multifunctional parts, based on their geometry and material properties. The combination of fused filament fabrication (FFF) and direct ink writing (DIW) techniques, respectively involving thermoplastics and thermosetting polymers (or composites), often focuses on planar and small‐scale applications (i.e., few cm), with limited nozzle orientation freedom for the fabrication of complex parts. Many industries, such as the aerospace sector, could benefit from the AM of lightweight multifunctional parts. For instance, one of the key aircraft components, the abradable seal coating, is applied on gas turbine engines casing to increase engine efficiency and is mechanically abraded by the rotor blades during engine startup. Abradable coatings made of thermosetting polymer could be 3D‐printed using a multiprocess to obtain more functionalities. In this work, a non‐planar multiprocess AM approach involving FFF of a complex large sandwich panel structure with low material density and large‐scale DIW of an abradable thermosetting coating with controlled porosity for sound absorption potential, and better mechanical abradability than a commercial product, is presented. This multiprocess AM approach can be used to manufacture lightweight multifunctional structural parts for the automotive or aerospace industries.

Crossover from Positive to Negative Spin Hall Signal in a Ferromagnetic Metal Induced by the Magnetization Modulated Interface Effect

AbstractThe spin Hall effect and its inverse (SHE/ISHE), describing the charge‐to‐spin interconversion, are of critical importance to the fundamental physics involving spin‐orbit coupling and the application of spintronic devices. These phenomena in nonmagnetic materials are reasonably understood after extensive studies. In ferromagnetic metals, however, the fundamental issue of generation and transport of pure spin current, especially the interplay of charge‐to‐spin interconversion and magnetization, is as‐yet poorly understood. Here, direct experimental evidence for the sign change in ISHE by injecting a spin current from Y3Fe5O12 into a Fe film via a Cu spacer is reported. The sizable negative ISHE signal (VISHE) in nanometer‐thick Fe films reverses its sign with a comparable magnitude when Fe magnetization is varied from a longitudinal to transverse orientation with respect to spin current polarization. With decreasing Fe thickness, this negative longitudinal VISHE increases rapidly to a larger positive value in magnitude. The opposite spin Hall angles for longitudinally and transversely polarized spin currents are reproduced by first‐principles transport calculations and the sign change is attributed to the anisotropic contribution at the ferromagnetic interface. This work lays a firm foundation for manipulating spin‐to‐charge interconversion with an extra degree of freedom of magnetization orientation through ferromagnetic metals.

Detecting and characterizing phase transitions in active matter using entropy.

A major challenge in the study of active matter lies in quantitative characterization of phases and transitions between them. We show how the entropy of a collection of active objects can be used to classify regimes and spatial patterns in their collective behavior. Specifically, we estimate the contributions to the total entropy from correlations between the degrees of freedom of position and orientation. This analysis pin-points the flocking transition in the Vicsek model while clarifying the physical mechanism behind the transition. When applied to experiments on swarming Bacillus subtilis with different cell aspect ratios and overall bacterial area fractions, the entropy analysis reveals a rich phase diagram with transitions between qualitatively different swarm statistics. We discuss physical and biological implications of these findings.

Oriented attachment kinetics for rod-like particles at a flat surface: Buffon's needle at the nanoscale.

The adsorption of large rod-like molecules or crystallites on a flat crystal face, similar to Buffon's needle, requires the rods to "land," with their binding sites in precise orientational alignment with matching sites on the surface. An example is provided by long, helical antifreeze proteins (AFPs), which bind at specific facets and orientations on the ice surface. The alignment constraint for adsorption, in combination with the loss in orientational freedom as the molecule diffuses toward the surface, results in an entropic barrier that hinders the adsorption. Prior kinetic models do not factor in the complete geometry of the molecule, nor explicitly enforce orientational constraints for adsorption. Here, we develop a diffusion-controlled adsorption theory for AFP molecules binding at specific orientations to flat ice surfaces. We formulate the diffusion equation with relevant boundary conditions and present analytical solutions to the attachment rate constant. The resulting rate constant is a function of the length and aspect ratio of the AFP, the distance threshold associated with binding, and solvent conditions such as temperature and viscosity. These results and methods of calculation may also be useful for predicting the kinetics of crystal growth through oriented attachment.

Limitations of the Right to Respect Private Life in the Regulation of the Romanian Civil Code

The protection of private life came into attention both at national and international level starting from the idea that this concept overlaps in many aspects with a person’s life concept: private life, with reference to freedom of sexual orientation, surveillance of the person, family life, the right to the inviolability of domicile, of correspondence (written, telephone or electronic), protection of personal data. Human dignity and free development of human personality constitute supreme values of the constitutional state and the vector of all interpretations of legal provisions – foundation of the universality of human rights and liberties. The Romanian Civil Code and other regulations in the field of audiovisual provide actual regulations for violating the right to private life and indirectly establish the legal limits of this right.

Low-temperature resistance of fluorine rubber with modified Si-based nanoparticles

Fluorine rubber contains fluorine atoms with strong electronegativity, which endow it with novel properties, such as oil resistance, heat resistance, chemical resistance, but also lead to poor low temperature resistance. Si-based nanoparticles are used as the new active crosslinking point of fluorine rubber, which can break the original regular structure to improve the low-temperature resistance and ensuring the mechanical properties of fluorine rubber. The relative optimal silane coupling agent is selected according to the relative concentration and the interaction energy of the molecular interface in different models. The optimal silane coupling agent can avoid the agglomeration of Si-based nanoparticles in fluorine rubber and form flexible bridge between inorganic Si-based nanoparticles and fluorine rubber long chains. It is discovered that the mechanical and low-temperature properties of the modified Si-based nanoparticles/fluorine rubber (FKM-M Si) was optimal compared with pure fluorine rubber (P-FKM) and unmodified Si-based nanoparticles/fluorine rubber (FKM-UM Si). The brittleness temperature (T b ) is reduced from -18.0 °C to -29.0 °C, allowing for a wider range of applications for FKM-M Si. This study provided a potential for the application of fluorine rubber composites in harsh low-temperature environment. • The silicon nanoparticles have larger Si–O–Si bond angles, high orientation freedom and good flexibility. • Improving the dispersion of silicon nanoparticles in fluorine rubber by chemical modification. • Unique nanocomposite structure is the key point of the low temperature resistance.

Non-Globular Organic Ionic Plastic Crystal Containing a Crown-Ether Moiety - Tuning Its Behaviour Using Sodium Salts.

Organic ionic plastic crystals (OIPCs) are a class of soft materials showing positional order while still allowing orientational freedom. Due to their motional freedom in the solid state, they possess plasticity, non‐flammability and high ionic conductivity. OIPC behavior is typically exhibited by ‘simple’ globular molecules allowing molecular rotation, whereas the interactions that govern the formation of OIPC phases in complex non‐globular molecules are less understood. To better understand these interactions, a new family of non‐globular OIPCs containing a 15‐crown‐5 ether moiety was synthetized and characterized. The 15C5BA molecule prepared does not exhibit the sought‐after behavior because of its non‐globular nature and strong intermolecular H‐bonds that restrict orientational motion. However, the OIPC behavior was successfully obtained through complexation of the crown‐ether moiety with sodium salts containing chaotropic anions. Those anions weaken the interactions between the molecules, allowing rotational freedom and tuning of the thermal and morphological properties of the OIPC.

The Structure of Water in Silica Mesopores – Influence of the Pore Wall Polarity

AbstractIn the spatial confinement of cylindrical mesopores with diameters of a few nanometers, water molecules experience restrictions in hydrogen bonding. This leads to a different behavior regarding the molecular orientational freedom (‘structure of water') compared to the bulk liquid state. In addition to the pore size, the behavior is also strongly affected by the strength of the pore wall‐to‐water interactions, that is, the pore wall polarity. In this work, this is studied both experimentally and theoretically. The surface polarity of mesoporous silica (SiO2) is modified by functionalization with trimethylsilyl moieties, resulting in a change from a hydrophilic (pristine) to a hydrophobic pore wall. The mesopore surface is characterized by N2 and H2O sorption experiments. Those results are combined with IR spectroscopy to investigate pore wall‐to‐water interactions leading to different structures of water in the mesopore. Furthermore, the water's structure is studied theoretically to gain deeper insight into the interfacial interactions. For this purpose, the structure of water is analyzed by pairing densities, coordination, and angular distributions with a novel adaptation of surface‐specific sum‐frequency generation calculation for pore environments.

Mesophase Transitions in [(C2H5)4N][FeBrCl3] and [(CH3)4N][FeBrCl3] Ferroic Plastic Crystals

Plastic crystals are supramolecular materials that possess a unique high entropy mesophase at elevated temperatures, where a long-range structural symmetry coexists with a local molecular orientational disorder. The transition to mesophase can involve a large entropy change useful for thermal energy storage and influences the temperature range of ferroelectric and piezoelectric properties, important for sensor applications. Synchrotron X-ray diffraction and pair distribution function analysis were used to study the structure, while calorimetry, dielectric, leakage current measurements, and density functional theory were used to investigate the influence of the organic cation on the structure and properties of tetraethylammonium bromotrichloroferrate(III) [(C2H5)4N][FeBrCl3] and tetramethylammonium bromotrichloroferrate [(CH3)4N][FeBrCl3]. The [(C2H5)4N][FeBrCl3] mesophase transition had an entropy change of 151.5 J·K–1·kg–1, while [(CH3)4N][FeBrCl3] had only 49 J·K–1·kg–1. This was explained by the [(C2H5)4N][FeBrCl3] mesophase having less long-range structural symmetry and more local orientational disorder, of both the cations and anions, compared to [(CH3)4N][FeBrCl3]. Both materials exhibited at least two conductive mechanisms below the transition, vacancy-mediated ionic and electronic conduction. The introduction of anion orientational freedom, as opposed to cation orientational freedom, at the mesophase transition was most influential for the electrical properties.

Squeezing Out Interfacial Solvation: The Role of Hydrogen-Bonding in the Structural and Orientational Freedom of Molecular Self-Assembly.

Bioinspired membrane molecules with improved physical properties and enhanced stability can serve as functional models for conventional lipid or amphiphilic species. Importantly, these molecules can also provide new insights into emergent phenomena that manifest during self-assembly at interfaces. Here, we elucidate the structural response and mechanistic steps underlying the self-assembly of the amphiphilic, charged oligodimethylsiloxane imidazolium cation (ODMS-MIM+) at the air-aqueous interface using Langmuir trough methods with coincident surface-specific vibrational sum-frequency generation (SFG) spectroscopy. We find evidence for a new compression-induced desolvation step that precedes commonly known disordered-to-ordered phase transitions to form nanoscopic assemblies. The experimental data was supported by atomistic molecular dynamics (MD) simulations to provide a detailed mechanistic picture underlying the assembly and the role of water in these phase transitions. The sensitivity of the hydrophobic ODMS tail conformations to compression─owing to distinct water-ODMS interactions and tail-tail solvation properties─offers new strategies for the design of interfaces that can be further used to develop soft-matter electronics and low-dimensional materials using physical and chemical controls.

Analysis of rotation capacity of a novel 2R1T mechanism based on origami of thick panels

A foldable and symmetrical lower-mobility parallel mechanism was proposed based on Waterbomb origami of thick panels. It consists of a moving platform, a base plate and three deployable foldable legs between moving platform and base plate. Firstly, constraint wrenches of each leg were formulated based on screw theory and the results illustrated that the moving platform is in possession of two degrees of orientation freedom and one translational degree of freedom. Secondly, it was approved that base and moving platform are always symmetrical about a middle plane and the moving platform can rotate continuously about any axis chosen freely on this plane. Solving models including forward and inverse position problems were established to determine the maximum rotational angle and workspace. Finally, performance indexe of maximum rotational angle of the PM was analyzed, and effects of two structural variables to the performance were summarized. Conclusions obtained can provide a theoretical basis for the structural design and engineering application of this 2T1R parallel mechanism.

Supercritical anomalies in liquid ODIC-forming cyclooctanol under the strong electric field

The evidence for long-range pretransitional effects in the liquid phase of ODIC-forming cycloctanol is presented. ODIC means ‘orientationally disordered crystal’, i.e. the plastic crystalline material in which translation freezing in a crystalline network coexists with the orientational freedom. The mentioned result was obtained using two methods inherently associated with the strong electric field: Electrooptic Kerr Effect (EKE) and Nonlinear Dielectric Effect (NDE). The model-analysis revealed the weakly discontinuous character of ODIC←Liquid phase transition and the possibility of a unified description with the isotropic – nematic/smectic transitions in rod-like liquid crystalline compounds. The extension to precritical effects near the critical consolute point and the gas–liquid critical point is indicated. Results obtained can be considered a potential base for the new generation of supercritical technologies, using ODIC- forming liquids with properties controlled by the electric field.