Degrees Of Freedom Research Articles

Enhancing grasping capabilities through a three-finger gripper with full degrees of freedom

Enhancing grasping capabilities through a three-finger gripper with full degrees of freedom

Local Temperature Measurement in Molecular Dynamics Simulations with Rigid Constraints.

Constraining molecules in simulations (such as with constant bond lengths and/or angles) reduces their degrees of freedom (DoF), which in turn affects temperature calculations in those simulations. When local temperatures are measured, e.g., from a set of atoms in a subvolume or from velocities in one Cartesian direction, the result can appear to unphysically violate equipartition of the kinetic energy if the local DoF are not correctly calculated. Here, we determine how to correctly calculate local temperatures from arbitrary Cartesian component kinetic energies, accounting for general geometric constraints, by self-consistently evaluating the DoF of atoms subjected to those constraints. The method is validated on a variety of test systems, including systems subject to a temperature gradient and those confined between walls. It is also shown to provide a sensitive test for the breakdown of kinetic energy equipartition caused by the approximate nature of numerical integration or insufficient equilibration times. As a practical demonstration, we show that kinetic energy equipartition between C and H atoms connected by rigid bonds can be violated even at the commonly used time step of 2 fs and that this equipartition violation appears to usefully indicate configurational overheating.

Degrees of Freedom: Rethinking Higher Education Credentials in South Africa

The shifting landscape of higher education and the labour market has necessitated re-evaluating conventional degree programmes, leading to an exploration of macro-credentialing as a link between university offerings and industry requirements. This paper examines the traditional dominance of the degree and the concurrent rise of strategic partnerships between higher education institutions and businesses, with the goal of developing credentials more closely aligned with the dynamic needs of the modern workforce. Traditionally, university degrees have been viewed as the bedrock of educational achievement and a prerequisite for professional success. However, rapid technological advancements and changing economic demands have exposed limitations in the degree model, particularly its often inflexible curriculum and lengthy completion time. Consequently, there is growing interest, especially within Private higher education, in macro-credentialing, which encompasses an array of non-degree awards that can be directly linked to specific skill sets and employment opportunities. Through qualitative analysis of partnership models across diverse industries and countries, this study identifies core elements contributing to the successful integration of macro-credentials into educational and professional spheres. These elements include co-creating curricula (between industry and the university), shared governance structures between educational and corporate entities, and robust assessment methodologies that validate learner competencies consistent with industry standards. Additionally, the study explores potential challenges and resistance within academia and industry, including credential recognition issues, balancing theoretical knowledge versus practical skills, and economic impacts on traditional degree pathways. It proposes strategic approaches to mitigate these challenges, emphasising the importance of transparency, stakeholder engagement, and continuous evaluation. The incorporation of macro-credentialing via university (both public and private), TVET college and Community College - Business partnerships possesses considerable potential to tackle future student discipline trajectories, the dire unemployment of South African youth and the growing needs of upskilling via life-long learning. It demands continuous innovation in educational models to guarantee they promote individual career achievements and societal progress in an increasingly intricate global economy. This paradigm transition from the conventional degree to a more adaptable, competency-based credentialing structure signifies a crucial development in matching education and industry.

Improving student learning outcomes and perception through a blended learning strategy based on virtual microscopy for teaching a histology laboratory course.

While light microscopy (LM) and virtual microscopy (VM) are valuable pedagogical approaches in histology education, studies comparing their effectiveness have primarily emanated from North America. This research aimed to compare the performance, satisfaction, and perception of Chinese undergraduate dental students enrolled in a histology laboratory course using a blended learning approach (LM+VM) versus traditional LM learning. A total of 182 first-year students were divided into two groups with similar age, gender, and academic backgrounds. The LM+VM group received a blended learning curriculum combining LM and VM, while the LM-only group participated in traditional LM-based learning. The students in the blended learning group achieved a significantly higher mean score on the laboratory exam than the students in the traditional learning group (LM+VM 79.36 ± 10.11 vs. LM-only 74.76 ± 14.71; degrees of freedom (df) = 180, P = 0.01). Additionally, the LM+VM group had a lower failure rate (i.e., grade F for students scoring below 60) (3.23% [LM+VM] vs. 13.48% [LM-only], P = 0.02). The implementation of VM was well-received by students in the LM+VM group, who, while disagreeing that VM could entirely replace LM, overwhelmingly preferred the blended learning model (93.55%). Furthermore, students in the LM+VM group reported higher satisfaction levels compared to the LM-only group (t = 8.49, df = 180, P < 0.001). Overall, blended learning with LM and VM resulted in significant improvements in student performance, satisfaction, and perception compared to traditional LM learning.

Influence of resonant plasmonic nanoparticles on optically accessing the valley degree of freedom in 2D semiconductors

The valley degree of freedom in atomically thin transition metal dichalcogenides, coupled with valley-contrasting optical selection rules, holds great potential for future electronic and optoelectronic devices. Resonant optical nanostructures emerge as promising tools for controlling this degree of freedom at the nanoscale. However, their impact on the circular polarization of valley-selective emission remains poorly understood. In our study, we explore a hybrid system where valley-specific emission from a molybdenum disulfide monolayer interacts with a resonant plasmonic nanosphere. Contrary to the simple intuition that a centrosymmetric nanoresonator mostly preserves the degree of circular polarization, our cryogenic experiments reveal significant depolarization of the photoluminescence scattered by the nanoparticle. This striking effect presents an ideal platform for studying the mechanisms governing light-matter interactions in such hybrid systems. Our full-wave numerical analysis provides insights into the key physical mechanisms affecting the polarization response, offering a pathway toward designing novel valleytronic devices.

Minimum time connection between non-equilibrium steady states: the Brownian gyrator

Abstract We study the problem of minimising the connection time between non-equilibrium steady states of the Brownian gyrator. This is a paradigmatic model in non-equilibrium statistical mechanics, an overdamped Brownian particle trapped in a two-dimensional elliptical potential, with the two degrees of freedom (x, y) coupled to two, in principle different, thermal baths with temperatures Tx and Ty , respectively. Application of Pontryagin’s Maximum Principle reveals that shortest protocols belong to the boundaries of the control set defined by the limiting values of the parameters (k, u) characterising the elliptical potential. We identify two classes of optimal minimum time protocols, i.e. brachistochrones: (i) regular bang–bang protocols, for which (k, u) alternatively take their minimum and maximum values allowed, and (ii) infinitely degenerate singular protocols. We thoroughly investigate the minimum connection time over the brachistochrones in the limit of having infinite capacity for compression. A plethora of striking phenomena emerge: sets of states attained at null connection times, discontinuities in the connection time along adjacent target states, and the fact that, starting from a state in which the oscillators are coupled, uncoupled states are impossible to reach in a finite time.

Implementation of the UNRES/SUGRES-1P Coarse-Grained Model of Heparin for Simulating Protein/Heparin Interactions.

Heparin is a natural highly sulfated unbranched periodic polysaccharide that plays a critical role in regulating various cellular events through interactions with its protein targets such as growth factors and cytokines. Although all-atom simulations of heparin-containing systems provide valuable insights into their structural and dynamical properties, long chains of heparin participate in many biologically relevant processes at much bigger scales and longer times than the ones which all-atom MD is able to effectively deal with. Among these processes is the establishment of chemokine gradients, amyloidogenesis, or collagen network organization. To address this limitation, coarse-grained models simplify these systems by reducing the number of degrees of freedom, allowing for the efficient exploration of structural changes within protein/heparin complexes. We introduce and validate the accuracy of a new coarse-grained physics-based model designed for studying protein/heparin interactions, which has been incorporated into the UNRES software package. The effective energy functions from UNRES and SUGRES-1P have been employed for the protein and heparin components, respectively. A good agreement between the obtained coarse-grained simulation results and experimental data confirms the suitability of the combined coarse-grained UNRES and SUGRES-1P model for in silico analysis of complex biological phenomena involving heparin, spanning time scales and molecular system sizes not attainable by conventional atomistic molecular dynamics simulations.

Engineering the Coherent Phonon Transport in Polar Ferromagnetic Oxide Superlattices.

Artificial superlattices composed of perovskite oxides serves as an essential platform for engineering coherent phonon transport by redefining the lattice periodicity, which strongly influences the lattice-coupled phase transitions in charge and spin degrees of freedom. However, previous methods of manipulating phonons have been limited to controlling the periodicity of superlattice, rather than utilizing complex mutual interactions that are prominent in transition metal oxides. In this study onoxide superlattices composed of ferromagnetic metallic SrRuO3 and quantum paraelectric SrTiO3, phonon modulation by controlling the geometry of superlattice in atomic-scale precision is realized, demonstrating the coherent phonon engineering using structural and magnetic phase transitions. By modulating the interface density, coherent-incoherent crossover of the phonon transport at room temperature is observed, which is coupled with a change in interfacial structural continuity. Upon cooling, the close relation between phonon transport and multiple phase transitions is identified. In particular, the enhancement of the polar state in SrTiO3 layer at ≈200K leads to the weakening of phonon coherence and a further reduction of thermal conductivity in superlattices compared to the bulk limit. These findings provide a guide to developing future thermoelectric nanodevices by engineering the coherence of phonons via the design of complex oxide heterostructures.

A multiverse model in T2 dS wedge holography

We construct a multiverse model where empty AdSd+1 space is cut off by a pair of accelerated dSd space universes, at a finite AdS boundary cutoff which we treat as a T2 deformation in the holographic dual, and one in the AdS interior, the IR brane; and denote the construction as T2 dS wedge holography. We glue together several copies of this configuration along the UV cutoff and the IR branes in a periodic matter. To provide the model with dynamics similar to those of near Nariai black holes used in other multiverse toy models, we specialize to d = 2 and add dS JT gravity as an intrinsic gravity theory on the IR branes. We then study the entanglement entropy with respect to a finite cutoff observer, who finds a Page curve transition due to an entanglement island connecting the UV cutoff and IR brane. This process involves the coarse-graining of information outside the causally accessible region to the observer. Our model provides an explicit realization of entanglement between IR and UV degrees of freedom encoded in the multiverse.

Intrinsically Ties Adjusted Median Test for Determining the Lengths of Hospitalization of Sampled Patients with Hypertension and Malaria in A Population

Background: This paper proposes and presents a nonparametric statistical method for the analysis of two sample data that intrinsically and structurally adjusts the test statistic, for the possible presence of tied observations in the sample populations. Methodology: The proposed procedure makes it unnecessary to require the populations to be continuous as is often the case with some other methods. The populations may be measurement on as low as the ordinal scale and need not be continuous or even numeric. In situations where the original or initial null hypothesis is rejected, test statistics are developed to help determine which of the two populations of interest may be responsible for the rejection of the null hypothesis, an approach that is not possible for some other existing two sample median test. Results: The proposed method is illustrated with some sample data and shown using the data to compare favorably with the usual median test and the Mann-Whitney U-test that could be used for the same purpose. Result showed that we rejected the null hypothesis, that hypertension and malaria patients from the population admitted to a hospital for treatment do not have equal median lengths of hospitalization for hypertension and malaria. Since The Chi-square value for testing the null hypothesis that the median length of hospitalization of hypertension patients in the population is equal to the median length of hospitalization of both hypertension and malaria patients in the population when pooled together as one population, is which with 1 degree of freedom is not statistically significant at the 5 percent significance level leading to the non-rejection of the null hypothesis. the Chi-Square value for testing the same null hypothesis with respect to malaria patients, that is that the median length of hospitalization of malaria patients in the population is the same as the median length of hospitalization of the combined or pooled population of hypertension and malaria patients when combined and treated as one population is which with 1 degree of freedom is statistically significant at the 5 percent significance level leading to the rejection of the null hypothesis. Conclusions and recommendations: We conclude that hypertension and malaria patients in the population do not have equal median lengths of hospitalization. We may therefore conclude that the median length of hospitalization of malaria patients is statistically different from the median length of hospitalization of both hypertension and malaria patients in the sampled population and may hence be responsible for the rejection of the initial null hypothesis H0 of Equation 11 or 12 of equal population median lengths of hospitalization of the two types of patients in the sampled population. since the Chi-square value of obtained using the proposed modified ties adjusted median test for two samples is much larger than the Chi-square value of obtained using the usual ordinary unmodified ties unadjusted two sample median test, the proposed method is likely to correctly reject a false null hypothesis more often and hence is more powerful than the ordinary median test when used to analyze the same sample observations.

Data‐Driven Kinematic Modeling of Physical Origami Robots

Origami‐inspired structures facilitate the design of compliant and compact robots. However, physical origami robots possess inherent material compliance and mechanical imperfections, presenting challenges in modeling and redundant actuation for accurate control of all degree of freedom (DoF). Herein, a data‐driven kinematic modeling approach tailored for physical origami robots to effectively address the inherent compliance is introduced. This approach is applied to a multiloop origami spherical joint, which features a minimalistic design comprising two parallel waterbomb structures. This design allows for the integration of four actuators, thereby enabling full control over the structure's three DoF and its inherent compliance. It is demonstrated that a small dataset is adequate for accurately learning the forward kinematics, which then informs an optimization‐based inverse kinematics. Additionally, through trajectory tracking experiments, it is verified that the modeling method is both rapid and accurate, making it suitable for real‐time applications. To showcase a practical application, the joint and its models are utilized as a force feedback origami joystick, designed for intuitive drone control. This joystick offers an enhanced control experience and conveys crucial information about collisions and external forces to drone operators. Overall, the data‐driven modeling approach introduces a new possibility of designing controllable compliant interfaces.

Assessing the impact of Niger Delta Development Commission interventions on road construction and economic activities in Cross River and Akwa Ibom States, Nigeria

Road construction and maintenance are key interventions that support economic potential in the country. However, the deplorable state of some roads in Nigeria, and in Cross River and Akwa Ibom states draws research concerns. This paper seeks to examine the impact of the Niger Delta Development Commission Intervention on road construction and economic activities in Cross River and Akwa Ibom States, Nigeria. Using the Sustainable Development Framework, a survey research design was employed, gathering data from 400 respondents across both states. The chi-square statistical technique was used to test the hypothesis that the Niger Delta Development Commission Intervention has no significant impact on road construction in Akwa Ibom and Cross River States. The result of the data analysis showed the calculated value X2 = 1592 &gt; 16.92. By this result, the null hypothesis was rejected (16.92) at 0.05 level of significance and 9 Degrees of Freedom, and the alternate was accepted. The study concludes that NDDC road projects have positively influenced economic activities and livelihoods in the states. However, it highlights the need for further improvements, particularly on the Calabar-Itu federal highway.

Experimental study on the acoustic roughness spectrum of high-speed railway rails

PurposeThis study aims to investigate the acoustic roughness of rails on China’s high-speed railways, with a focus on short-wavelength irregularities (less than 80 cm), which are known to significantly contribute to noise. The goal is to develop a specific acoustic roughness spectrum tailored for China’s high-speed railway system, as no such spectrum currently exists.Design/methodology/approachA long-term tracking study was conducted on major railway lines in China, monitoring rail roughness throughout the initial operational period and the rails’ service life. Data preprocessing techniques such as peak removal and curvature correction were applied for acoustic adjustments. A spatial-wavelength domain transformation was performed, providing the distribution patterns and statistical characteristics of acoustic roughness on China’s high-speed rails. Based on these analyses, a model for constructing the acoustic roughness spectrum was developed.FindingsThe study found that the acoustic roughness of China’s high-speed railway rails follows a χ2 distribution with six degrees of freedom. For wavelengths greater than 8 cm, the acoustic roughness spectrum remains below the ISO specified limits. In the wavelength range of 3.2 cm to 6.3 cm, the roughness is comparable to or within the limits specified by ISO 3095:2005 and ISO 3095:2013. However, for wavelengths shorter than 2.5 cm, the roughness exceeds ISO limits.Originality/valueThis research fills the gap in the lack of a specific acoustic roughness spectrum for China’s high-speed railways. By establishing a tailored spectrum based on long-term data analysis, the findings provide valuable insights for noise control and rail maintenance in the context of China’s high-speed rail system.

Height Measurement for Meter-Wave MIMO Radar Based on Sparse Array Under Multipath Interference

For meter-wave multiple-input multiple-output (MIMO) radar, the multipath of target echoes may cause severe errors in height measurement, especially in the case of complex terrain where terrain fluctuation, ground inclination, and multiple reflection points exist. Inspired by a sparse array with greater degrees of freedom and low mutual coupling, a height measurement method based on a sparse array is proposed. First, a practical signal model of MIMO radar based on a sparse array is established. Then, the modified multiple signal classification (MUSIC) and maximum likelihood (ML) estimation algorithms based on two classical sparse arrays (coprime array and nested array) are proposed. To reduce the complexity of the algorithm, a real-valued processing algorithm for generalized MUSIC (GMUSIC) and maximum likelihood is proposed, and a reduced dimension matrix is introduced into the real-valued processing algorithm to further reduce computation complexity. Finally, sufficient simulation results are provided to illustrate the effectiveness and superiority of the proposed technique. The simulation results show that the height measurement accuracy can be efficiently improved by using our proposed technique for both simple and complex terrain.

Displacement-Based Seismic Design of Multi-Story Resistance Capacitance-Coupled Shear Wall Buildings with Energy-Dissipation Dampers

This research aims to apply the displacement-based design method (DBDM) for the seismic design of reinforced concrete-coupled shear wall buildings equipped with energy dissipation dampers. The DBDM offers design simplicity by focusing on structural design based on a target design displacement, where the building converts into a single degree of freedom (SDOF) system. The implementation of dampers aims to reduce repair costs and downtime for buildings following significant seismic events. Two types of dampers are utilized in this study: metallic damper and viscoelastic damper. The DBDM procedure begins with determining the target displacement, which corresponds to the specific story drift ratio of the structural system, using a nonlinear static pushover analysis. For the structural wall system considered in this study, a target drift ratio of 1/250 is selected due to the inherent rigidity of the structure. The effective damping factor is then determined from the average energy absorption, which is based on the ductility factor of each structural member. Additionally, the effective period of the building is obtained from the displacement spectrum of the design-level earthquakes. Finally, the required damper shear capacity for the SDOF system is calculated based on the target deformation and effective stiffness. The design earthquakes are generated from the acceleration response spectrum for Level 2 earthquakes, as specified in the Japanese seismic code, utilizing three different sets of phase information: Kobe, El Centro, and random phase records. The effectiveness of the DBDM is scrutinized through a comparison with results obtained from time history analysis. The results obtained for 6-, 12-, and 18-story RC-coupled shear walls with energy dissipation dampers indicate that the proposed design methodology effectively meets the specified design objectives.

Optical skyrmions and tunable fine spin structures in deep-subwavelength scale at metal/graded index material interfaces

A skyrmion is a topological quasiparticle that has been studied widely in nuclear physics, condensed matter physics, cosmology, and optics. Previously, the optical skyrmions in the surface plasmon polaritons platform were not tunable because the dielectric properties of the material were fixed. In the study, we introduce the graded refractive index materials into the near-field optical system and systematically investigate the propagation properties, dispersion relations, and spin-orbit decomposition of the surface waves at the metal/graded refractive index materials interface. Our theoretical results exhibit that the topological spin skyrmions can be formed in the system and the dimensions of optical skyrmions can be tuned by varying the central permittivity and exponent of the graded refractive index materials. Additionally, the spin fine structure, in which the spin state varies sharply from the ‘up’ state to the ‘down’ state, can be also controlled by adjusting the materials properties of the graded refractive index materials. The minimal full width of the spin fine structure is 0.254λ, which has the potential for achieving the displacement metrology with a sensitivity of 2.54 × 10−7λ theoretically. Our findings provide an extra degree of freedom to control the formation and scale of fine spin structures in optical skyrmions and open an avenue for next-generation pico-photonics.

Analysis of mooring performance and layout parameters of multi-segment mooring system for a 15 MW floating wind turbine

IntroductionFloating wind power is the important path for the development of offshore wind energy, and the performance of the mooring system of floating wind turbines (FOWTs) significantly affects their economic viability, safety, and sustainability.MethodsThis paper systematically analyses the positioning performance, mooring line extreme loads, and fatigue response of a FOWT equipped with both single segment and multi-segment mooring systems, based on the IEA 15 MW large turbine and a floating platform. The hydrodynamic performance of the floating platform is calculated, and the platform’s motion-sensitive directions are analysed through Response Amplitude Operators (RAOs). The natural periods of the platform are validated by free decay tests. The six degrees of freedom (DOFs) motion response and the mooring line peak tensions are analysed under normal and extreme conditions.ResultsThe results show that both mooring systems provide good motion performance and stable tilt angles for the platform. Under ALS (single-line failure) condition, the multi-segment mooring system demonstrates a notable capacity to resist impact loads, with comparatively minor fluctuations in mooring line tension. In the multi-segment system, fatigue damage primarily occurs in the upper mooring chain, with damage approximately 4.5 times greater than that of the bottom chain over a 1-year period. The effects of mooring line spread angles and lengths on performance are also analysed. The results indicate that the mooring line spread angle has slight impact on platform motion response and mooring line tension, while mooring line length significantly affects the extreme tension of the lines.DiscussionThe findings of this study can provide some references in the design of mooring systems for future FOWTs.

Electrical Tortuosities of Porous Structures Based on Triply Periodic Minimal Surfaces and Honeycombs for Power-to-Heat Systems

Power-to-heat (P2H) systems offer an efficient solution for decarbonization by facilitating the integration of renewable energy into the industrial, heating, and transport sectors. Its key requirements include high thermal efficiency and an appropriate electrical resistivity to meet application-specific electrical needs. When designing P2H systems, materials and electrical boundary conditions are often limited by application-specific requirements, whereas geometric structures offer high degrees of freedom. While thermal design calculations are often straightforward due to a variety of available Nusselt and pressure loss correlations, simplified design pathways, particularly for porous structures, are lacking in electrical design. Given the wide range of geometric degrees of freedom for porous structures and the fact that detailed modeling involves substantial computational effort, this work employed electrical tortuosity to capture and correlate the geometry-dependent impacts on the effective electrical resistance in a compact way. Honeycomb and triply periodic minimal surface (TPMS)-based structures were selected for this purpose, as they are characterized by high specific surfaces, allowing for high total heat transfer coefficients. The results show that the effective electrical resistance of both TPMS and honeycomb structures can be adjusted by the geometric structure. It was found that the electrical tortuosities of the investigated TPMS structures are nearly identical, while honeycomb structures show slightly higher values. Furthermore, the electrical tortuosity is mainly a function of the void fraction and does not change with the specific surface when the void fraction is kept constant. Finally, correlations for electrical tortuosity depending on geometric parameters with a mean error below 5% are derived for the first time, thereby providing a basis for simplified and computationally efficient electrical design calculations for P2H systems.

Quad mesh mechanisms

This paper provides computational tools for the modeling and design of quad mesh mechanisms, which are meshes allowing continuous flexions under the assumption of rigid faces and hinges in the edges. We combine methods and results from different areas, namely differential geometry of surfaces, rigidity and flexibility of bar and joint frameworks, algebraic geometry, and optimization. The basic idea to achieve a time-continuous flexion is time-discretization justified by an algebraic degree argument. We are able to prove computationally feasible bounds on the number of required time instances we need to incorporate in our optimization. For optimization to succeed, an informed initialization is crucial. We present two computational pipelines to achieve that: one based on remeshing isometric surface pairs, another one based on iterative refinement. A third manner of initialization proved very effective: We interactively design meshes which are close to a narrow known class of flexible meshes, but not contained in it. Having enjoyed sufficiently many degrees of freedom during design, we afterwards optimize towards flexibility.

U-shaped disks in Stokes flow: chiral sedimentation of a non-chiral particle

We study the sedimentation of U-shaped circular disks in the Stokes limit of vanishing inertia. We simulate the flow past such disks using a finite-element-based solution of the three-dimensional Stokes equations, accounting for the integrable singularities that develop along their edges. We show that the purely vertical sedimentation of such disks in their upright (upside-down) U orientation is unstable to perturbations about their pitching (rolling) axes. The instability is found to depend only weakly on the size of the container in which the disks sediment, allowing us to analyse their behaviour based on the resistance matrix which governs the evolution of the disk's six rigid-body degrees of freedom in an unbounded fluid. We show that the governing equations can be reduced to two ordinary differential equations which describe the disk's inclination against the direction of gravity. A phase-plane analysis, the results of which are in good agreement with experiments, reveals that the two instabilities generally cause the disk to sediment along complex spiral trajectories while it alternates between pitching- and rolling-dominated motions. The chirality of the trajectories is set by the initial conditions rather than the (non-chiral) shape of the disk. For certain initial orientations, the disk retains its inclination and sediments along a perfectly helical path. The observed behaviour is fundamentally different from that displayed by flat circular disks which sediment without any reorientation. We therefore study the effect of variations in the disk's curvature to show how in the limit of vanishing curvature the behaviour of a flat disk is recovered.