Initial Rotation Research Articles

Flexural behaviour of bolted flange-plate with bonded sleeve splice connections for pultruded GFRP circular tubular hollow beams

The paper presents an experimental and finite element investigation of bolted flange-plate with bonded sleeve splice connections for joining pultruded glass fibre-reinforced polymer (GFRP) circular tubular beams. The moment-rotation behaviour was investigated in terms of initial rotational stiffness, moment capacity and rotation capacity for all the tested splice connections. The effect of the number of flange-plate bolts, flange-plate thickness and the length of the bonded sleeve were examined. Failure modes for the thinner flange-plates included opening, bending and yielding of the flange-plates in the tension zone. Thicker flange-plates and a higher number of bolts exhibited improved initial rotational stiffness with lower rotational capacity, which can be enhanced by higher bonded sleeve lengths. Available design codes for steel joints were used to classify the splice connections with regards to rigidity and strength. The failure modes from the finite element models were consistent with the experimental observations, which includes the plastic deformation of the flange-plate and the cohesive failure of the adhesive.

Field oriented control driver development based on BTS7960 for physiotherapy robot implementation

In conjunction with sustainable development goal 3 (SDG 3), it is important to develop a national electrical component for physiotherapy robot development. This study aimed to develop an open-loop field-oriented control (FOC) driver utilizing BTS7960. The driver utilized three BTS7960s that produce sinewave with variable angular frequency (ω). The research then compared the open-loop FOC driver with electronics speed controller (ESC) performance to drive a brushless DC (BLDC) motor with an initial rotation per minute (RPM) of 400, 500, and 600. The main observation was RPM reduction when the BLDC motor was subjected to loads of 20, 35, 50, 65, and 80 gr. The result showed that the open-loop FOC driver performed better, especially on an 80 gr load. For an initial RPM of 600, the RPM reduced to 100 when controlled with an open-loop FOC driver, but lesser when controlled using ESC. The open-loop FOC driver produces higher torque on the BLDC motor so it could rotate with less reduction compared to ESC, which is evident. The open-loop FOC driver can be easily developed using BTS7960 with a settling time of 4 seconds. However future studies should still consider close-loop FOC drivers to achieve higher torque performance and faster transient response for physiotherapy robot applications.

A two-dimensional perspective of the rotational evolution of rapidly rotating intermediate-mass stars

Context. Recently, the first successful attempt at computing stellar structure and evolution models in two dimensions was presented with models that include centrifugal deformation and self-consistently compute the velocity field. Aims. The aim of the present study is to explore the rotational evolution of two-dimensional models of stars rotating at a significant fraction of their critical angular velocity. From the predictions of these models, we aim to improve our understanding of the formation of single Be stars. Methods. Using the ESTER code, which solves the stellar structure of a rotating star in two dimensions with time evolution, we computed evolution tracks of stars of between 4 and 10 M⊙ for initial rotation rates ranging between 60 and 90% of the critical rotation rate. Furthermore, we compute models for both a Galactic metallicity and an SMC metallicity. Results. A minimum initial rotation rate at the start of the main sequence is needed to spin up the star to critical rotation within its main sequence lifetime. This threshold depends on the stellar mass, and increases with increasing mass. The models do not predict any stars above 8 M⊙ to reach (near-)critical rotation during the main sequence. Furthermore, we find the minimum threshold of initial angular velocity is lower for SMC metallicity than for Galactic metallicity, which is in agreement with the increased fraction of observed Be stars in lower metallicity environments. The strong difference in the rotational evolution between different masses is not predicted by any one-dimensional stellar evolution models. Conclusions. Our self-consistent two-dimensional stellar evolution models provide further insight into the rotational evolution of intermediate-mass stars, and our predictions are consistent with observations of velocity distributions and the fraction of Be stars amongst B-type stars. We find that stars with a mass above 8 M⊙ do not increase their fraction of critical rotation during the main sequence. As a fraction of stars above 8 M⊙ have been observed to display the Be phenomenon, other processes or formation channels must be at play, or, alternatively, critical rotation is not required for the Be phenomenon above this mass.

Experimental investigation on inter-particle settling dynamics of multiple spherical particles released side by side at intermediate Reynolds numbers

The settling of solid particles in fluid constitutes a fundamental and crucial aspect with applications spanning various natural phenomena and engineering processes, including sediment transport and wastewater treatments. This paper delves into an experimental investigation aimed at comprehending the settling dynamics and self-organization of multiple spherical particles settling side by side at intermediate Reynolds numbers. The study employs an electromagnetic release device, previously developed for controlled settling of particles under gravity, ensuring simultaneous release with zero initial rotation and velocity. This research captures settling trajectories and provides insight into the flow fields surrounding particles by utilizing particle tracking and particle image velocimetry. The experiments systematically investigate the influence of the settling patterns, the flow fields, the velocities of particles, and their dependence on Reynolds number Re (Re = 52–258), the number of particles n (n = 3–8), as well as the initial spacing between particles l0* (l0* = 0–2). The results consistently reveal a left–right symmetry about the centerline in settling patterns, flow fields, and particle rotations across all values of n, l0*, and Re. The final settling pattern exhibits distinct shapes dependent on l0*: a “V” or “M” shape for l0* < 0.2, a “concave-downward” shape for 0.2 < l0* < 2, and a “straight-line” shape for l0* ≥ 2. The lateral spread of particles increases with time, particularly pronounced with smaller l0* and larger Re, attributed to strong repulsive forces between neighboring particles. Correspondingly, the maximum of horizontal velocities reduces from outside to inside and increases with decreasing l0* and increasing Re. The inner vortices are smaller than the outer vortices, which causes the lateral spread. The vertical spread increases with n but remains insensitive to Re. The average terminal settling velocities for all particles in the array are consistently smaller than those for single particles, as a portion of kinetic energy contributes to horizontal motions.

Stable fixation of an ultra-short femoral neck-preserving hip prosthesis: a 5-year RSA, DXA, and clinical prospective outcome study of 48 patients.

We previously showed promising primary stability and preservation of bone stock with the ultra-short neck-loading hip implant in total hip arthroplasty (THA). The aim of this study was to evaluate clinical outcome, implant stability, and bone mineral density (BMD). 50 patients were treated with the ultra-short neck Primoris hip implant at baseline and 48 were available for evaluation at 5-year follow-up. 5 different patient-reported outcome measures (PROMs) including hip-specific scores, disease-specific and generic quality of life outcome measures, and an activity score were used. Furthermore, implant stability using radiostereometric analysis (RSA) and assessment of periprosthetic BMD using dual-energy X-ray absorptiometry (DXA) were applied. By 1-year follow-up, all PROMs showed improvements and remained high at 5-year follow-up. After initial distal translation (subsidence) and negative rotation around the z-axis (varus tilt) the implant showed stable fixation at 5-year follow-up with no further migration beyond 12 months. In the regions of interest (ROI) 3 and 4, BMD remained stable. In ROI 2, further bone loss of 12% was found at 5-year follow-up. Clinical outcome including PROMs was satisfying throughout the 5-year follow-up period. The hip implant remains stable with both bone preservation and loss 5 years after surgery.

Isotope Effect and Heavy-Light-Heavy Reactivity Oscillation in the Cl + CHD3/CHT3 Reaction.

Previous experiments and theories have shown the existence of heavy-light-heavy (HLH) reactivity oscillation in the Cl + CH4 reaction and anticipated that similar oscillations should exist in many HLH reactions involving polyatomic reagents. However, the total reaction probabilities for the Cl + CHD3 → HCl + CD3 reaction exhibit only a step-like feature, and the total reaction probabilities for Cl + CHT3 → HCl + CT3 do not show any structure at all. Here, we report seven-dimensional state-to-state quantum dynamics studies for this reaction on the FI-NN PES, and we demonstrate that HLH reactivity oscillations also exist in these two reactions, manifesting as peaks in the reaction probabilities for low product rotational states. These oscillations, however, are obscured in the total reaction probability because of the higher excitation of j ≥ 2 product rotational states. Furthermore, the isotope replacement of nonreactive hydrogen with deuterium and tritium significantly enhances reactivity at collision energies above 0.112 eV, indicating an inverse secondary isotope effect on the probabilities, which is proved to be also caused by HLH mass combination. We also demonstrate that the highly rotational excitation of CHD3 substantially enhances reactivity and the HLH oscillations, similar to HLH triatomic reactions. These observations are completely different from those in the H + CHD3 reaction, which is also a late-barrier reaction. Therefore, the HLH mass combination is very important, which affects not only the reactivity oscillation but also the amplitude and product rotational state distribution and makes the initial rotation excitation play a pivotal role in the reaction.

Energy spectra and fluxes of turbulent rotating Bose–Einstein condensates in two dimensions

We investigate the scaling of the energy cascade in a harmonically trapped, turbulent, rotating Bose-Einstein condensate in two dimensions. We achieve turbulence by injecting a localized perturbation into the condensate and gradually increasing its rotation frequency from an initial value to a maximum. The main characteristics of the resulting turbulent state depend on the initial conditions, rotation frequency, and ramp-up time. We analyze the energy and the fluxes of kinetic energy by considering initial profiles without vortices and with vortex lattices. In the case without initial vortices, we find the presence of Kolmogorov-like scaling (k−5/3) of the incompressible kinetic energy in the inertial range. However, with initial vortex lattices, the energy spectrum follows Vinen scaling (k−1) at transient iterations. For cases with high rotating frequencies, Kolmogorov-like scaling emerges at longer durations. We observe positive kinetic energy fluxes with both initial states across all final frequencies, indicating a forward cascade of incompressible and compressible kinetic energy.

Zero and Extremely Low-metallicity Rotating Massive Stars: Evolution, Explosion, and Nucleosynthesis Up to the Heaviest Nuclei

We present the evolution and the explosion of two massive stars, 15 and 25 M ⊙, spanning a wide range of initial rotation velocities (from 0 to 800 km s−1) and three initial metallicities: Z = 0 ([Fe/H] = −∞), 3.236 × 10−7 ([Fe/H] = −5), and 3.236 × 10−6 ([Fe/H] = −4). A very large nuclear network of 524 nuclear species extending up to Bi has been adopted. Our main findings may be summarized as follows: (a) rotating models above Z = 0 are able to produce nuclei up to the neutron closure shell N = 50, and in a few cases up to N = 82; (b) rotation drastically inhibits the penetration of the He convective shell in the H-rich mantle, a phenomenon often found in zero metallicity nonrotating massive stars; (c) vice versa, rotation favors the penetration of the O convective shell in the C-rich layers with the consequence of significantly altering the yields of the products of the C, Ne, and O burning; (d) none of the models that reach the critical velocity while in H burning lose more the 1 M ⊙ in this phase; (e) conversely, almost all models able to reach their Hayashi track exceed the Eddington luminosity and dynamically lose almost all their H-rich mantle. These models suggest that rotating massive stars may have contributed significantly to the synthesis of the heavy nuclei in the first phase of enrichment of the interstellar medium, i.e., at early times.

Nursing students’ perceptions of older adults, confidence, and anxiety level changes with their first clinical rotation: A descriptive pilot study

Nursing students often hesitate to work with older adults due to a lack of knowledge and preconceived notions. Students also experience increased anxiety and lack confidence in assessment and communication skills. This study is a descriptive pilot study to examine nursing students' perceptions towards older adult care, anxiety levels, and confidence in nursing care skills before and after their initial clinical rotation in a long-term care facility to develop future supportive educational programs and studies. 70 first-semester baccalaureate nursing students from a single nursing college answered five Likert scale questions through an online survey link. Results showed a significant increase in students' confidence in assessment and communication skills, and a decrease in anxiety after the clinical. However, students' willingness to work with older adults did not significantly change and was even lower than before the clinical. The positive sentiment of caring for older adults increased by 5.6%, negative sentiment decreased by 0.9%, and neutral sentiment decreased by 4.7%. Clinical education should prioritize strategies to reduce pre-clinical anxiety, emphasize the significance of working with older adults, and address barriers to enhance students' perceptions and attitudes toward this population.

Evaluation of a Serrated Edge to Mitigate the Adverse Effects of a Backward-Facing Step on an Airfoil

Backward-facing steps are commonly formed on wings and blades due to misalignment between segments or the addition of protective films. A backward-facing step (BFS) is known to degrade the airfoil performance. To mitigate these adverse effects, a three-dimensional low-profile serrated pattern (termed sBFS) was applied downstream of a BFS on an LA203A profile airfoil. The model drag was determined from wake surveys using a traversing Pitot-static probe within a subsonic wind tunnel operating at a chord-based Reynolds number of 300,000. The airfoil spanned the wind tunnel width (914 mm) and had a 197 mm chord length. Four different sBFS configurations were tested, each formed by applying a 1 mm thick film around the model leading edge. In addition, a BFS at various chord locations and a clean wing (i.e., no film applied) were tested for reference. The sBFS was able to reduce the drag relative the BFS by up to 8–10%, though not outperforming the clean wing configuration. In addition, the wake surveys showed the sBFS produced strong coherent structures that persist into the far-wake region (five chord length downstream of the model) with a scale that was much larger than the step height. Additionally, a computational study was carried out to further examine the flow behavior on the airfoil that produced the coherent structures. This showed that fluid near the surface gets entrained towards the sBFS downstream tip of the sBFS, which creates the initial rotation of these coherent structures that persist into the far-wake region.

FUNCTIONAL STABILITY OF THE INVERTED PENDULUM AND ITS RELATION TO UNCREWED AERIAL VEHICLE WINGS THROUGH SYSTEM MATHEMATICAL MODELING AND SIMULATION

The flight instability of an uncrewed aerial vehicle (UAV) can be considered critical, and investigations of stability can be compared to the study of the stabilization of an inverted pendulum. This study investigated the stability of two dynamic systems, represented by an inverted pendulum and a simple approximation of an aircraft wing surface exposed to aerodynamic forces. This study illustrates the advantages of time-domain simulation for solving the differential equation of motion. The simulation used the Euler integration approach for various system parameters. Essentially, an aircraft in flight must constantly maintain pitch stability, which, in practical considerations, can be compared to the mechanism of a rotary motion represented by the up-swinging motion of an inverted pendulum. The pendulum may conserve the same concept as an aircraft’s acceleration, as both are affected by the same gravity and acceleration forces, in which the longitudinal stability of the aircraft must be ensured immediately upon takeoff. An inverted pendulum and a UAV aircraft system simulation were developed with basic MATLAB software. The inverted pendulum simulation showed that as the value of the spring’s stiffness at the limit of stability (klim) increased, the system became more convergent and, as a result, more stable. The stiffness of the spring at the limit of stability, klim = 32.69 N m-1 (i.e., equivalent to an initial angular rotation θ = 5 °), and the system’s stability were observed up to the value of klim = 179.79 N m-1, which resulted in an unstable short initial period. In addition, for the aircraft’s wing, the damping coefficient (clim) value was in the range of clim ≥ 10,000 N s m-1. Therefore, with the damping ratio ζ being equal to zero, the system vibrated consistently at its natural frequency (wn), never deviating drastically to become unstable.

The young massive SMC cluster NGC 330 seen by MUSE

Context. The origin of the initial rotation rates of stars, and how a star’s surface rotational velocity changes during the evolution, either by internal angular momentum transport or due to interactions with a binary companion, remain open questions in stellar astrophysics. Aims. Here, we aim to derive the physical parameters and study the distribution of (projected) rotational velocities of B-type stars in the ∼35 Myr-old, massive cluster NGC 330 in the Small Magellanic Cloud. NGC 330 is in an age range where the number of post-interaction binaries is predicted to be high near the cluster turnoff (TO). Methods. We developed a simultaneous photometric and spectroscopic grid-fitting method adjusting atmosphere models on multiband Hubble Space Telescope (HST) photometry and Multi Unit Spectroscopic Explorer (MUSE) spectroscopy. This allowed us to homogeneously constrain the physical parameters of over 250 B and Be stars (i.e., B-type stars with emission lines), brighter than mF814W = 18.8 mag. Results. The rotational velocities of Be stars in NGC 330 are significantly higher than the ones of B-type stars. The rotational velocities vary as a function of the star’s position in the color-magnitude diagram, qualitatively following predictions of binary population synthesis. A comparison to younger clusters shows that stars in NGC 330 rotate more rapidly on average. Conclusions. The rotational velocities of the ∼35 Myr old population in NGC 330 quantitatively agree with predictions for a stellar population that underwent significant binary interactions: the majority of the B-type stars could be single stars or primaries in pre-interaction binaries. The rapidly spinning Be stars could be mass and angular momentum gainers in previous interactions, while those Be stars close to the TO may be spun-up single stars. The slowly rotating, apparently single stars above the TO could be merger products. The different v sin i characteristics of NGC 330 compared to younger populations can be understood in this framework.

The impact of convective criteria on the properties of massive stars

Context. Libraries of stellar models computed with either the Ledoux or the Schwarzschild criterion to determine the sizes of convective regions are available in the literature. It is still not clear, however, which of these two criteria should be used, although many works have been devoted to that question in the past. Aims. In the framework of the evolution of single rotating stars, we study the differences between models computed with Ledoux and Schwarzschild criteria on the internal structure, evolutionary track in the Hertzsprung–Russell diagram (HRD), lifetimes, evolution of the surface abundances and velocities, and masses of the He and CO cores. We investigate the consequences on the nature of the supernova (SN) progenitors and the type of SN events, as well as on the stellar yields of light elements. We also study the impact on the outputs of population synthesis models. Methods. Models with initial masses between 7 and 120 M⊙ at solar metallicity (Z = 0.014) and with an initial rotation equal to 0 or 0.4 times the critical velocity at the zero-age main sequence were computed with either the Schwarzschild or the Ledoux criterion until the end of the C-burning phase. Results. Models with initial masses between 15 and 32 M⊙ computed with the Schwarzschild criterion show larger intermediate convective zones attached to the H-burning shell than models computed with the Ledoux criterion. Their CO cores and outer convective zones in the red supergiant (RSG) phase are also smaller. This impacts many outputs of stars during the core He-burning phase. Schwarzschild models have smaller CO cores and outer convective zones in the RSG phase, and their blue-to-red supergiant ratio is much higher than for Ledoux models. They also produce longer crossings of the Hertzsprung gap and favour blue loops. The upper luminosity of RSGs is little affected by the change in the convective criterion. The maximum luminosity of RSG progenitors for type II-P SN events is lowered from 5.2 to 4.95 when the Ledoux criterion is used instead of the Schwarzschild criterion in non-rotating models. The Schwarzschild criterion predicts longer-lasting, less nitrogen-enriched, and faster-rotating Cepheids. Rotational mixing tends to decrease the differences between Schwarzschild and Ledoux models. Conclusions. The results of this paper can be used as first guidelines to set up observational programs that may help to distinguish between these two model families.

Characterizing the Directionality of Gravitational Wave Emission from Matter Motions within Core-collapse Supernovae

We analyze the directional dependence of the gravitational wave (GW) emission from 15 3D neutrino radiation hydrodynamic simulations of core-collapse supernovae (CCSNe). Using spin weighted spherical harmonics, we develop a new analytic technique to quantify the evolution of the distribution of GW emission over all angles. We construct a physics-informed toy model that can be used to approximate GW distributions for general ellipsoid-like systems, and use it to provide closed form expressions for the distribution of GWs for different CCSN phases. Using these toy models, we approximate the protoneutron star (PNS) dynamics during multiple CCSN stages and obtain similar GW distributions to simulation outputs. When considering all viewing angles, we apply this new technique to quantify the evolution of preferred directions of GW emission. For nonrotating cases, this dominant viewing angle drifts isotropically throughout the supernova, set by the dynamical timescale of the PNS. For rotating cases, during core bounce and the following tens of milliseconds, the strongest GW signal is observed along the equator. During the accretion phase, comparable—if not stronger—GW amplitudes are generated along the axis of rotation, which can be enhanced by the low T/∣W∣ instability. We show two dominant factors influencing the directionality of GW emission are the degree of initial rotation and explosion morphology. Lastly, looking forward, we note the sensitive interplay between GW detector site and supernova orientation, along with its effect on detecting individual polarization modes.

Complex Neck Loading and Injury Tolerance in Lateral Bending With Head Rotation From Human Cadaver Tests.

Advancements in automated vehicles may position the occupant in postures different from the current standard posture. It may affect human tolerance responses. The objective of this study was to determine the lateral bending tolerance of the head-cervical spine with initial head rotation posture using loads at the occipital condyles and lower neck and describe injuries. Using a custom loading device, head-cervical spine complexes from human cadavers were prepared with load cells at the ends. Lateral bending loads were applied to prerotated specimens at 1.5 m/s. At the occipital condyles, peak axial and antero-posterior and medial-lateral shear forces were: 316-954 N, 176-254 N, and 327-508 N, and coronal, sagittal, and axial moments were: 27-38 N·m, 21-38 N·m, and 9.7-19.8 N·m, respectively. At the lower neck, peak axial and shear forces were: 677-1004 N, 115-227 N, and 178-350 N, and coronal, sagittal, and axial moments were: 30-39 N·m, 7.6-21.3 N·m, and 5.7-13.4 N·m, respectively. Ipsilateral atlas lateral mass fractures occurred in four out of five specimens with varying joint diastasis and capsular ligament involvements. Acknowledging that the study used a small sample size, initial tolerances at the occipital condyles and lower neck were estimated using survival analysis. Injury patterns with posture variations are discussed.

Reinforcement Learning With Stereo-View Observation for Robust Electronic Component Robotic Insertion

In modern manufacturing, assembly tasks are a major challenge for robotics. In the manufacturing industry, a wide range of insertion tasks can be found, from peg-in-hole insertion to electronic parts assembly. Robotic stations designed for this problem often use conventional hybrid force-position control to perform preprogrammed trajectories, such as e.g. a spiral path. However, electronic parts require more sophisticated techniques due to their complex geometry and susceptibility to damage. Production line assembly tasks require high robustness to initial position and rotation variations due to component grip imperfections. Robustness to partially obscured camera view is also mandatory due to multi stage assembly process. We propose a stereo-view method based on reinforcement learning (RL) for the robust assembly of electronic parts. Applicability of our method to real-world production lines is verified through test scenarios. Our approach is the most robust to applied perturbations of all tested methods and can potentially be transferred to environments unseen during learning.

The Effect of Roll Circular Vection on Roll Tilt Postural Responses and Roll Subjective Postural Horizontal of Healthy Normal Subjects.

Background: Falls and related injuries are critical issues in several disease states, as well as aging, especially when interactions between vestibular and visual sensory inputs are involved. Slow support surface tilt (0.6 deg/s) followed by subjective postural horizontal (SPH) assessments have been proposed as a viable method for assessing otolith contributions to balance control. Previous assessments of perceived body alignment to vertical, including subjective visual vertical, have suggested that visual inputs are weighted more when vestibular information is near the threshold and less reliable during slow body tilt. To date, no studies have examined the influence of visual stimuli on slow roll-tilt postural responses and the SPH. Therefore, this study investigated how dynamic visual cues, in the form of circular vection (CV), influence postural responses and the perception of the horizontal during and after support surface tilt. Methods: Ten healthy young adults (6 female, mean age 23) wore a head-mounted display while standing on a tilting platform. Participants were asked to remain upright for 30 s, during which (1) the visual scene rotated, inducing roll CV clockwise (CW) or counter-clockwise (CCW) at 60°/s; (2) the platform only (PO) rotated in roll to test SPH (0.6°/s, 2°, CW or CCW); (3) a combination of both; or (4) neither occurred. During SPH trials, participants used a hand-held device to reset the position of the platform to 0.8°/s to their perceived SPH. The angular motion of body segments was measured using pairs of light-emitting diodes mounted on the head, trunk and pelvis. Segment motion, prior to platform motion, was compared to that at peak body motion induced by platform motion and when SPH had been set. Results: When the support surface was tilted 2°, peak upper body tilt significantly increased for congruent CV and platform tilt and decreased at the pelvis for incongruent CV when compared to PO, leading to significant differences across body segments for congruent and incongruent conditions (p ≤ 0.008). During PO, participants' mean SPH deviated from horizontal by 0.2°. The pelvis deviated 0.2°, the trunk 0.3°, and the head 0.5° in the direction of initial platform rotation. When platform tilt and CV directions were congruent or incongruent, only head tilt at SPH reset under congruent conditions was significantly different from the PO condition (1.7° vs. 0.5°). Conclusions: Roll CV has a significant effect on phasic body responses and a less significant effect on tonic body responses to lateral tilt. The SPH of the support surface was not altered by CV. Responses during tilt demonstrated enhanced reactions for congruent and reduced reactions for incongruent CV, both different from responses to CV alone. Tonic body displacements associated with SPH were changed less than those during tilt and were only slightly larger than displacements for CV alone. This study supports the hypothesis of weighted multisensory integration during dynamic postural tasks being highly dependent on the direction of visual cues during tilt and less dependent on tonic SPH offsets. These techniques could be used to examine vestibular and visual interactions within clinical populations, particularly those with visual vertigo and dizziness.

Experimental investigation of rotational behavior of pseudo-ductile adhesive angle joints exhibiting variable strain rate

Pseudo-ductile behavior in composite structural frames can be achieved by enabling their beam-column joints to exhibit nonlinear structural response due to progressive damage, by using pseudo-ductile adhesives. This study investigates the static behavior of a novel pseudo-ductile bonded-bolted angle joint with a bolt at the geometric centroid of the joint. A pseudo-ductile elastomer adhesive is used which is notably sensitive to the strain rate. The bolt ensures structural integrity and produces pure torsional moments in the adhesive planes. This configuration induces nonuniform strain rates in the adhesive layers in the radial direction, i.e., from the center outwards. The experimental results reveal that under the nonuniform shear strain distribution, the initial stiffness, yield rotation, and maximum torsion exhibit an increasing trend with strain rate, while maximum rotation decreases. An analytical model was developed using stress-strain relations obtained from single-lap joints with uniform stress distribution to predict the angle joint responses. The analytical model overestimates the initial joint stiffness due to the nonuniform stress distribution but shows good agreement for strength and post-yield behavior. Lastly, the angle joint exhibits the lowest ductility ratios compared to linear lap joints, showing that the pseudo-ductile adhesive capacity may not be fully utilized in the angle configuration.

Fitting the Light Curve of 1I/‘Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques

In this paper, we investigate the nonprincipal axis (NPA) rotational state of 1I/‘Oumuamua—the first interstellar object discovered traversing the inner solar system—from its photometric light curve. Building upon Mashchenko, we develop a model which incorporates NPA rotation and Sun-induced, time-varying outgassing torques to generate synthetic light curves of the object. The model neglects tidal forces, which are negligible compared to outgassing torques over the distances at which ‘Oumuamua was observed. We implement an optimization scheme that incorporates the NPA rotation model to calculate the initial rotation state of the object. We find that an NPA rotation state with an average period of 〈P〉 ≃ 7.34 hr best reproduces the photometric data. The discrepancy between this period and previous estimates is due to continuous period modulation induced by outgassing torques in the rotational model, as well as different periods being used. The best fit to the 2017 October data does not reproduce the 2017 November data (although the later measurements are too sparse to fit). The light curve is consistent with there being no secular evolution of the angular momentum, which is somewhat in tension with the empirical correlations between nuclear spin-up and cometary outgassing. The complex rotation of ‘Oumuamua may be the result of primordial rotation about the smallest principal axis if (i) the object experienced hypervolatile outgassing and (ii) our idealized outgassing model is accurate.

Experimental and numerical investigation of bolted steel endplate with bonded sleeve end connections for pultruded GFRP circular tubular hollow beams

The paper presents an experimental and numerical investigation of bolted steel endplates with bonded sleeve connections developed for connecting pultruded glass fibre-reinforced polymer (GFRP) circular tubular beams. The moment-rotational responses were investigated in detail in terms of initial rotational stiffness, moment capacity, and rotation capacity for all the connections. The effect of endplate thickness and bonded sleeve length was also investigated. Predominant failure modes include bending and yielding of thinner endplates, while thicker endplates with low bonded sleeve lengths exhibit splitting failure in the bonded GFRP beam region. Available design codes for steel joints were used to classify the developed connections in terms of rigidity and strength. The failure modes from the finite element models were well matched by the experimental observations, which include the deformation of the endplate and the cohesive failure within the bonded sleeve region with the GFRP beam.