Symmetry Force Research Articles

Newtonian wormholes with spherical symmetry and tidal forces on test particles

A spherically symmetric wormhole in Newtonian gravitation in curved space, enhanced with a connection between the mass density and the Ricci scalar, is presented. The wormhole, consisting of two connected asymptotically flat regions, inhabits a spherically symmetric curved space. The gravitational potential, gravitational field and the pressure that supports the fluid that permeates the Newtonian wormhole are computed. Particle dynamics and tidal effects in this geometry are studied. The possibility of having Newtonian black holes in this theory is sketched.

Preliminary Evaluation of Toe–Heel and Mediolateral Hoof Balance at the Walk in Sound Horses With Toed-In Hoof Conformation

Empirically, toed-in hoof conformation has been associated with an increased risk of lameness and reduced longevity of equine athletes, presumably linked with changes in hoof balance. Therefore, toe–heel and mediolateral hoof balance of the vertical ground reaction force and limb-loading symmetry were objectively evaluated in five clinically sound, toed-in warmblood horses using a pressure plate. Five measurements of each forelimb were recorded at walk, and toe–heel and mediolateral hoof balance of the vertical ground reaction force were calculated throughout stance (126 Hz). Peak vertical force (PVF) and vertical impulse (VI) symmetry were calculated as lowest or highest mean value × 100%. All horses presented higher loading of the lateral zone at impact, rather equivalent loading of the medial and lateral zones at midstance, and increased lateral loading at the end of the stance phase in both forelimbs. Unexpectedly, left and right fore toe–heel balance in four of the five toed-in horses revealed higher loading of the toe zone at impact, whereas one horse presented higher loading of the heel zone at impact in both forelimbs. Limb-loading symmetry was 83.1 ± 8.7% and 84.1 ± 7.9% for PVF and VI, respectively, which was lower than expected in sound horses. It is unclear if the distinct difference in toe–heel balance compared with previously reported data in horses with normal distal limb conformation is actually predisposing to or is a consequence of pathology, but it may be associated with distal limb lameness, as increased loading of the toe early in the stance phase has been associated with navicular disease.

Knee Extensor Moment Asymmetry is Related to Modulation of GRFs During Gait Post-ACL Reconstruction

Clinically it is expected that individuals will restore normal gait mechanics by 3 months post anterior cruciate ligament reconstruction (ACLr). However, biomechanical studies at this time report that large knee extensor moment asymmetries are present in the absence of large kinematic differences. This suggests that individuals may be modulating ground reaction forces to limit knee loading. PURPOSE: To determine the relationship between knee extensor moment symmetry and ground reaction force and knee flexion angle symmetry between limbs during gait at 3 months post-ACLr. METHODS: 13 individuals (8 females, 24.2 ± 9.2 yrs) performed 3 walking trials at 3 months (87.9 ± 8.9 days) post-ACLr. 3D kinematics (250 Hz), ground reaction forces (1500Hz) and anthropometrics were used to quantify knee kinematics and kinetics (inverse dynamics) in the sagittal plane. Peak knee flexion angle (kFLEX), peak knee extensor moment (kEXT) and peak posterior (pGRF) and vertical (vGRF) ground reaction forces were identified during loading response. Between limb symmetry in kFLEX, kEXT, pGRF, and vGRF were calculated as the ratio between the involved and the uninvolved limbs. Pearson’s product-moment correlations were used to determine the relationship between knee loading deficits; significance α≤0.05. RESULTS: On average, kFLEX and kEXT ratios were 0.97 ± 0.18 (range: 0.72-1.34) and 0.77 ± 0.31 (range: 0.26-1.36) at 3 months, respectively. pGRF and kEXT ratios were correlated at 3 months (r=0.706; p=0.007). kEXT ratio was not correlated with vGRF ratio (r=0.290; p=0.337) or kFLEX ratio (r=0.440; p=0.132) at 3 months. CONCLUSIONS: Larger asymmetries in pGRF were strongly related to larger asymmetries in kEXT during gait at 3 months post-op, suggesting that smaller pGRFs are related to smaller kEXT. These data suggest that individuals post-ACLr modulate braking forces (pGRF), not vertical forces or knee flexion angle, to limit knee extensor moments during gait. Future studies should investigate how gait mechanics modulate braking force and sagittal plane knee loading and the mechanisms that underlie these movement patterns.

Network topology with broken Onsager symmetry allows directional and highly efficient energy transfer

Time-reversal symmetry of most conservative forces constrains the properties of linear transport in physical systems. Here, we study the efficiency of energy transfer in dissipative oscillator networks where time-reversal symmetry is broken locally by Lorentz-force–like couplings. Despite their linearity, such networks can exhibit mono-directional transport and allow isolation of energy transfer in subsystems. New mechanisms and general rules for mono-directional transport are discussed. Combining network topology with Lorentz-force–like coupling, we show how efficiency at maximum power can surpass the common bound of 1/2 and may even approach unity.

Does Computer-Assisted Femur First THR Improve Musculoskeletal Loading Conditions?

We have developed a novel, computer-assisted operation method for minimal-invasive total hip replacement (THR) following the concept of “femur first/combined anteversion,” which incorporates various aspects of performing a functional optimization of the prosthetic stem and cup position (CAS FF). The purpose of this study is to assess whether the hip joint reaction forces and patient's gait parameters are being improved by CAS FF in relation to conventional THR (CON). We enrolled 60 patients (28 CAS FF/32 CON) and invited them for gait analysis at three time points (preoperatively, postop six months, and postop 12 months). Data retrieved from gait analysis was processed using patient-specific musculoskeletal models. The target parameters were hip reaction force magnitude (hrf), symmetries, and orientation with respect to the cup. Hrf in the CAS FF group were closer to a young healthy normal. Phase-shift symmetry showed an increase in the CAS FF group. Hrf orientation in the CAS FF group was closer to optimum, though no edge or rim-loading occurred in the CON group as well. The CAS FF group showed an improved hrf orientation in an early stage and a trend to an improved long-term outcome.

Image comparisons among analysis, simulation and experimental solutions about stress distribution in rings loaded by multiple symmetrical radial forces

The theorem of energy valley state and a particular solution of Airy biharmonic equation will be used in the stress analysis in the rings loaded by the multiple- fold symmetrical forces to obtain stresses formulas. The varied stress graphs have been plotted with these formulas and FEM, revealing their periods of symmetry of forces.

Evaluation the immediate effects of bracing on kinetic parameters in adolescent idiopathic scoliosis patients

Background Idiopathic scoliosis induces change in coordination between body segments, spinal anatomy, left-right trunk symmetry and gait pattern. Various treatment methods have being used for scoliosis which includes: physical therapy, occupational therapy, osteopathic therapy, casting, bracing and surgery. However, using brace is a commonly used method in this regard. Although, the influence of brace to reduce the scoliosis curve has been investigated in lots of research studies, there is not enough research regarding the influence of brace on performance of scoliotic subjects while walking and standing. Therefore, the purpose of this study was to evaluate the immediate effect of brace on stability performance of scoliotic subjects and the symmetry of the ground reaction force applied on the right and left feet while walking. Method Then girls aged between 8 and 12 years were recruited in this study. The gait analysis was assessed using a three-dimensional motion analysis and a force plate (Kistler) in two conditions, with and without Boston brace. Moreover their stability was evaluated by use of force plate. The difference of kinetic and stability parameters between two conditions(with and without Boston brace)was checked by use of paired T-test. Results

Decentralized Positioning Algorithm for Relative Nodes Localization in Wireless Body Area Networks

Wireless Body Area Networks (WBAN) can offer motion capture capabilities through peer-to-peer ranging and on-body nodes positioning, by relying on transmitted signals and data packets. In this paper, we describe a solution to localize wireless nodes relatively to a body-strapped Local Coordinate System (LCS). In particular, we consider coupling a Constrained Distributed Weighted Multi-Dimensional Scaling algorithm (CDWMDS), which asynchronously estimates the nodes' locations under geometric constraints related to fixed-length links, with new messages censoring, location updates scheduling and forced measurements symmetry. The idea is to mitigate error propagation (e.g. with respect to the fastest nodes), as well as harmful effects caused by the loss of critical packets. We also introduce a real beacon-aided Time Division Multiple Access (TDMA) scheme to suitably support both peer-to-peer ranging and decentralized positioning transactions under real-time constraints. Simulation results are provided to assess the performance of the proposed solution for various levels of connectivity and ranging quality, showing interesting gains on the average location error per node under moderate pedestrian mobility. Comparisons are finally provided with a more conventional centralized and synchronous Multidimensional Scaling (MDS) algorithm that would require completing the matrix of measured distances under partial network connectivity.

Dynamical competition between quantum Hall and quantum spin Hall effects

In this paper we investigate the occurrence of quantum phase transitions in topological systems out of equi- librium. More specifically, we consider graphene with a sizable spin-orbit coupling, irradiated by circularly- polarized light. In the absence of light, the spin-orbit coupling drives a quantum spin Hall phase where edge currents with opposite spins counter-propagate. On the other hand, the light generates a time-dependent vector potential, which leads to a hopping parameter with staggered time-dependent phases around the benzene ring. The model is a dynamical version of the Haldane model, which considers a static staggered flux with zero total flux through each plaquette. Since the light breaks time-reversal symmetry, a quantum Hall phase protected by an integer topological invariant arises. By numerically solving the complete problem, with spin-orbit coupling and light, and investigating different values of the driving frequency {\omega}, we show that the spectrum exhibits non-trivial gaps not only at zero energy, but also at {\omega}/2. This additional gap is created by photon resonances between the valence and conduction band of graphene, and the symmetry of the spectrum forces it to lie at {\omega}/2. By increasing the intensity of the irradiation, the topological state in the zero energy gap undergoes a dynamical phase transition from a quantum spin Hall to a quantum Hall phase, whereas the gap around {\omega}/2 remains in the quantum Hall regime.

Knee Contact Force Asymmetries in Patients Who Failed Return-to-Sport Readiness Criteria 6 Months After Anterior Cruciate Ligament Reconstruction

Background: After anterior cruciate ligament (ACL) injury, contact forces are decreased in the injured knee when compared with the uninjured knee. The persistence of contact force asymmetries after ACL reconstruction may increase the risk of reinjury and may play an important role in the development of knee osteoarthritis in these patients. Functional performance may also be useful in identifying patients who demonstrate potentially harmful joint contact force asymmetries after ACL reconstruction. Hypothesis: Knee joint contact force asymmetries would be present during gait after ACL reconstruction, and performance on a specific set of validated return-to-sport (RTS) readiness criteria would discriminate between those who demonstrated contact force asymmetries and those who did not. Study Design: Descriptive laboratory study. Methods: A total of 29 patients with ACL ruptures participated in gait analysis and RTS readiness testing 6 months after reconstruction. Muscle and joint contact forces were estimated using an electromyography (EMG)–driven musculoskeletal model of the knee. The magnitude of typical limb asymmetry in uninjured controls was used to define limits of meaningful limb asymmetry in patients after ACL reconstruction. The RTS testing included isometric quadriceps strength testing, 4 unilateral hop tests, and 2 self-report questionnaires. Paired t tests were used to assess limb symmetry for peak medial and tibiofemoral contact forces in all patients, and a mixed-design analysis of variance was used to analyze the effect of passing or failing RTS testing on contact force asymmetry. Results: Among all patients, neither statistically significant nor meaningful contact force asymmetries were identified. However, patients who failed RTS testing exhibited meaningful contact force asymmetries, with tibiofemoral contact force being significantly lower for the involved knee. Conversely, patients who passed RTS testing exhibited neither significant nor meaningful contact force asymmetries. Conclusion: Joint contact force asymmetries during gait are present in some patients 6 months after ACL reconstruction. Patients who demonstrated poor functional performance on RTS readiness testing exhibited significant and meaningful contact force asymmetries. Clinical Relevance: When assessing all patients together, variability in the functional status obscured significant and meaningful differences in contact force asymmetry in patients 6 months after ACL reconstruction. These specific RTS readiness criteria appear to differentiate between those who demonstrate joint contact force symmetry after ACL reconstruction and those who do not.

Vacuum-induced symmetry breaking in a superconducting quantum circuit

The ultrastrong-coupling regime, where the atom-cavity coupling rate reaches a considerable fraction of the cavity or atom transition frequencies, has been reported in a flux qubit superconducting quantum circuit coupled to an on-chip coplanar resonator. In this regime situations may arise where the resonator field $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{X}=\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}+{\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{a}}^{\ifmmode\dagger\else\textdagger\fi{}}$ acquires a nonzero expectation value in the system ground state. We demonstrate that, in this case, the parity symmetry of an additional artificial atom with an even potential is broken by the interaction with the resonator. Such a mechanism is analogous to the Higgs mechanism where the gauge symmetry of the weak force's gauge bosons is broken by the nonzero vacuum expectation value of the Higgs field. The results presented here open the way to controllable experiments on symmetry-breaking mechanisms induced by nonzero vacuum expectation values. Moreover, the mechanism proposed here can be used as a probe of the ground-state macroscopic coherence emerging from quantum phase transitions with vacuum degeneracy.

Short communication: Changes in gait symmetry in healthy and lame dairy cows based on 3-dimensional ground reaction force curves following claw trimming

Lameness is a frequent health problem in dairy cows. This preliminary study aimed to detect gait differences between healthy and lame walking cows using 3-dimensional force plates. We examined left–right leg symmetry changes of healthy and lame Holstein dairy cows following claw trimming. Gait scoring (GS) was performed on d −5, 0, 1, and 7 relative to claw trimming. Before the experiment, 5 cows walked normally (initial GS=1) and 4 cows limped moderately on a hind leg (initial GS=3). Gait was measured on d −2, −1, 0, 1, and 7 relative to trimming by obtaining ground reaction forces as cows walked repeatedly across 2 parallel 3-dimensional force plates. From the ground reaction forces, stance phase data were derived using computerized procedures. Left–right leg symmetries of entire curves in the 3 force directions were calculated. Effects of lameness and trimming were analyzed in a mixed model, using a low lameness threshold (GS>1). One week after claw trimming, only one cow was mildly lame. In addition, the symmetries of all 3 dimensions were significantly improved shortly after trimming. Importantly, lameness significantly worsened vertical symmetry. Lame cows walked significantly more slowly than healthy cows. In conclusion, all force symmetries seemed capable of detecting gait responses to claw trimming. Although our results are based on a small number of animals, vertical leg symmetry was affected by lameness.

Spatial periodicity in bed form‐scale solute and thermal transport models of the hyporheic zone

AbstractSpatially periodic solute boundaries force symmetry across a model domain by ensuring that concentrations and concentration gradients are identical at the same location on opposite boundaries. They have been used in multiple publications on a hyporheic zone model of a single ripple or dune style bed form, including variable density flow and reactive transport variants. We evaluate simulations of multibed form models without imposing spatially periodic transport to demonstrate that nonphysical solute distributions arise from the periodic solute transport assumption. That is, the flow field within the single bed form model leads to a transport scenario that violates the forced symmetry of periodic solute boundary conditions, culminating in a physically unrealistic solute distribution. Our results show that lack of symmetry between boundaries is a function of the vertical concentration gradient and two‐dimensionless parameters characterizing the hyporheic and underflow flow regimes, and the solute exchange between them. We assess the error associated with the spatially periodic assumption based on an analysis of solute fluxes across the lateral bed form model boundaries. While the focus is on steady state concentration distributions, the implications for transient solute transport models are also discussed. We conclude that periodic solute transport boundary conditions should be applied only to bed form models that have minimal vertical dispersive and diffusive solute transfer. This includes gaining systems and tracers such as temperature, for which a temporally periodic flux reversal occurs across the top boundary.

The effect of total hip and hip resurfacing arthroplasty on vertical ground reaction force and impulse symmetry during a sit-to-stand task

BackgroundThe aim of this study was to determine the influence of total hip arthroplasty and hip resurfacing arthroplasty on limb loading symmetry before, and after, hip reconstruction surgery during a sit-to-stand task. MethodsFourteen patients were recruited that were about to receive either a total hip prosthesis (n=7) or a hip resurfacing prosthesis (n=7), as well as matched controls. Patients performed a sit-to-stand movement before, 3months after, and 12months after surgery. Peak vertical ground reaction force and impulse were measured for each leg, from which ground reaction force and impulse symmetry ratios were calculated. FindingsBefore surgery, hip resurfacing patients showed a small asymmetry which was not different to normal for ground reaction force (0.88(0.28) vs. 1.00(0.11); p=0.311) or impulse (0.87(0.29) vs. 0.99(0.09); p=0.324) symmetry ratios. Total hip patients offloaded their affected hip by 30% in terms of impulse symmetry ratio (0.71(0.36) vs. 0.99(0.23); p=0.018). At 3months following surgery asymmetries were seen that were different to normal in both hip resurfacing patients for ground reaction force (0.77(0.16); p=0.007), and total hip patients for ground reaction force (0.70(0.15); p=0.018) and impulse (0.72(0.16); p=0.011) symmetry ratios. By 12months after surgery total hip patients regained a symmetrical loading pattern for both ground reaction force (0.95(0.06); p=0.676) and impulse (1.00(0.06); p=0.702) symmetry ratios. Hip resurfacing patients, however, performed the task by overloading their operated hip, with impulse symmetry ratio being larger than normal (1.16(0.16); p=0.035). InterpretationPhysiotherapists should appreciate the need for early recovery of limb loading symmetry as well as subsequent differences in the responses observed with different prostheses.

Influence of minimally invasive total hip replacement on hip reaction forces and their orientations.

Minimally invasive surgery (MIS) is becoming increasingly popular. Supporters claim that the main advantages of MIS total hip replacement (THR) are less pain and a faster rehabilitation and recovery. Critics claim that safety and efficacy of MIS are yet to be determined. We focused on a biomechanical comparison between surgical standard and MIS approaches for THR during the early recovery of patients. A validated, parameterized musculoskeletal model was set to perform a squat of a 50th percentile healthy European male. A bilateral motion was chosen to investigate effects on the contralateral side. Surgical approaches were simulated by excluding the incised muscles from the computations. Resulting hip reaction forces and their symmetry and orientation were analyzed. MIS THR seemed less influential on the symmetry index of hip reaction forces between the operated and nonoperated leg when compared to the standard lateral approach. Hip reaction forces at peak loads of the standard transgluteal approach were 24% higher on the contralateral side when compared to MIS approaches. Our results suggest that MIS THR contributes to a greater symmetry of hip reaction forces in absolute value as well as force-orientation following THR.

Theoretical and Numerical Analysis on the Static-Loaded Contact Pressure of Mechanical Elastic Wheel

This paper describes the theoretical and numerical methods to calculate the contact pressure of Mechanical Elastic Wheel (MEW). The structure of MEW was introduced firstly, and then the contact pressure of MEW was calculated with the simplified model of a single layer composite ring according to Elasticity. Considering the structure and force symmetry, 1/2 finite element model of MEW was built. Mooney-Rivilin hyperelastic constitutive model was applied to simulate material nonlinearity, and frictionless contact type was applied to simulate nonlinear contact characteristics. With the Augmented Lagrangian solving method, the contact pressure analysis result of MEW was obtained. The theoretical and simulation values of MEW’s contact pressure are approximate with the deviation of 1.08%, and it indicates the validity of the simulation.

Determination of low-energy parameters of neutron-neutron scattering from an analysis of the binding-energy difference between the 3H and 3He mirror nuclei

A relation between quantities that characterize the breaking of the charge symmetry of nuclear forces in systems of two and three nucleons is found on the basis of an analysis of the binding-energy difference between the 3H and 3He mirror nuclei. For the neutron-neutron scattering length and effective range, the values of ann = −18.38(55) fm and rnn = 2.84(4) fm, respectively, were obtained by using purely nuclear parameters of proton-proton scattering in the 1S0 state. The calculated values agree with present-day experimental results.

Lead Limb Used During Drop Jumps Affects Initial Vertical Ground Reaction Force Symmetry

Lead Limb Used During Drop Jumps Affects Initial Vertical Ground Reaction Force Symmetry

Adsorption of Co and Ni on Graphene with a Double Hexagonal Symmetry: Electronic and Magnetic Properties

Inspired by Lie symmetries, we study the electronic and magnetic properties of cobalt (Co) and nickel (Ni) adatom adsorption on the graphene material using density functional theory calculations. The system we consider here consists of a static single layer of graphene interacting with transition-metal (TM) atoms. This system shows a nice geometrical shape having a double hexagonal structure appearing in the G2 Lie algebra. This structure is associated with 25% concentration corresponding to a coverage of 0.666 monolayers placed at H sites. This new symmetry forces the derived Co material to behave like a ferromagnetic metal with a strong spin polarization. However, the derived Ni material remains a nonmagnetic metal. For the Co case, we show that the magnetic mechanism responsible for such behavior is the interaction between the Co atoms. In fact, there are two interaction types. The first one is associated with the direct interaction between the Co atoms, while the second one corresponds to the indirect interaction via the carbon atoms. Using Monte Carlo simulation, the Curie temperature for the Co material is estimated to be around 438 K. This value could be explored in nanomagnetic applications.

Frameworks with forced symmetry II: orientation-preserving crystallographic groups

We give a combinatorial characterization of minimally rigid planar frameworks with orientation-preserving crystallographic symmetry, under the constraint of forced symmetry. The main theorems are proved by extending the methods of the first paper in this sequence from groups generated by a single rotation to groups generated by translations and rotations. The proof makes use of new families of matroids and submodular functions defined on crystallographic groups.