Obliquity Research Articles

Lattice Defects in Sub-Micrometer Spin-Crossover Crystals Studied by Electron Diffraction.

Spin-crossover particles of [Fe(Htrz)2trz](BF4) with sizes of some hundred nanometers are studied by in situ electron microscopy. Despite their high radiation sensitivity, it was possible to analyze the particles by imaging and diffraction so that a detailed analysis of crystallographic defects in individual particles became possible. The presence of one or several tilt boundaries, where the tilt axis is the direction of the polymer chains, is detected in each particle. An in situ exposure of the particles to temperature variations or short laser pulses to induce the spin crossover shows that the defect structure only changes after a high number of transformations between the low-spin and high-spin phases. The observations are explained by the anisotropy of the atomic architecture within the crystals, which facilitates defects between weakly linked crystallographic planes.

Stellar obliquity and planetary albedo in HAT-P-32

HAT-P-32 is an exceptional planetary system. Its active F-type host star is orbited by a hot Jupiter, the evaporation of which produces a giant structure of tidal tails. We analyze the light curve of HAT-P-32 obtained by the Transiting Exoplanet Survey Satellite (TESS) and find a secondary eclipse superimposed on photometric modulation likely caused by stellar rotation. We estimate a secondary eclipse depth of (1.4 ± 0.4)×10−4. Adopting a prior of 1962 ± 83 K for the effective planetary dayside temperature yields values of 0.16 ± 0.07 for the geometric albedo and an associated estimate of 0.46 ± 0.21 for the circulation efficiency of HAT-P-32 b, which favor a dark and windy scenario for the atmosphere. Our analysis of the photometric modulation yields a stellar rotation period of 2.974 ± 0.004 d, implying a value of 79° for the inclination of the stellar rotation axis with a 95% credible interval from 70° to 88°. This constraint further allows us to estimate a value of (84.9 ± 1.5)° for the three-dimensional obliquity. Despite showing an almost polar planetary orbit, the host star is, therefore, seen nearly equator on.

ASSESSMENT OF ESTHETIC SMILE COMPONENTS BY DENTAL STUDENTS

Background: The present information indicates that most students utilized the technology-based system well, but they missed some practical activities. Assessment of students’ satisfaction with the e-learning activities and asking for feedback can help institutions to improve the know-how about e-learning practices. Hopefully, the sudden pandemic-related shift through modes of education will not be considered an unfavorable impact on education but an evolving experience to pave a comprehensive way to technology-based educational activities.Material and methods: The study was performed on 580 dental students. Among the eight components of the balanced smile, six factors (the smile arc, smile line, dark buccal corridors, gingival margin and incisal edge asymmetries, tooth axis, and dental midline inclinations) apart from those related to dental and gingival ones, were examined on photographs. Manipulations were made on the photo of a female patient with the ideal smile.Results: Statistically significant differences were observed between the preclinical and clinical groups and, in binary comparisons, between curricular years at pre-clinical and clinical levels (P < 0.05).Conclusions: Our findings confirm the reports from previous investigations considering the impact of dental education on dental students’ perception of dentofacial esthetics.

Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph: Equatorial Latitudes in L Dwarf Atmospheres Are Cloudier

We report direct observational evidence for a latitudinal dependence of dust cloud opacity in ultracool dwarfs, indicating that equatorial latitudes are cloudier than polar latitudes. These results are based on a strong positive correlation between the viewing geometry and the mid-infrared silicate absorption strength in mid-L dwarfs using mid-infrared spectra from the Spitzer Space Telescope and spin axis inclination measurements from available information in the literature. We confirmed that the infrared color anomalies of L dwarfs positively correlate with dust cloud opacity and viewing geometry, where redder objects are inclined equator-on and exhibit more opaque dust clouds, while dwarfs viewed at higher latitudes and with more transparent clouds are bluer. These results show the relevance of viewing geometry to explain the appearance of brown dwarfs and provide insight into the spectral diversity observed in substellar and planetary atmospheres. We also find a hint that dust clouds at similar latitudes may have higher opacity in low-surface gravity dwarfs than in higher-gravity objects.

Effect of symmetrical and asymmetrical tilt grain boundaries with as the tilt axis on the shock response of bi-crystalline Ni

Aim of this article is to study the effect of tilt grain boundaries on the shock response of single and bi-crystalline nickel. Nickel is commonly used in many structural applications, but research on dynamic response is very limited or in an immature stage. In this article, molecular dynamics-based simulations were performed in conjunction with embedded atom method potential to quantify the response of shock in bi-crystalline Ni containing symmetrical or asymmetrical tilt grain boundaries. Simulations were performed under the influence of adiabatic conditions. Compressive ultra-shock pulse of width 2 ps was simulated in the simulation box; stress, particle velocity, dislocation emission and phase transformation were quantified for symmetrical and asymmetrical tilt grain boundaries in bi-crystalline Ni. It was concluded from the simulations that higher mis-orientation angle between the crystals of Ni help in retarding the shock front velocity and stress. The alternation in the shock front behavior was associated with the change in deformation governing mechanism. The emission of dislocations and formation of Lomer Cottrell lock governs deformation in symmetrical tilt grain boundary configurations under shock pulse loading. It was concluded from the set of simulations that plastic deformation blunts the shock front in bi-crystalline Ni, whereas the sharp shock front was observed in single crystal Ni. Radial distribution function in post shock atomistic configurations was performed to capture the stability of the crystal in post shock scenario. Asymmetrical tilt grain boundaries are not as efficient in restricting the shock front as symmetrical tilt grain boundary configurations.

Small-Perturbation Analysis of Airplane Dynamics With Dynamic Stability Derivatives Redefined

The first successful powered and controlled heavier-than-air flight and the subsequent meteoric rise of aviation in the 20th century also brought with it mathematical models to understand the phenomenon of flight. Though successful to a large extent as is obvious from their longevity, these models still suffer from the odd anomalous result. Upon careful examination, the source of this problem can be traced to an inappropriate choice of dynamic stability derivatives that is inconsistent with the aerodynamics. In order to correctly distinguish between the different mechanisms that are responsible for the aerodynamic forces and moments generated due to body angular rates in flight, this paper refines the existing model for flight mechanics by redefining the dynamic stability derivatives with respect to, i) relative rate of rotation between the body and wind axes, and ii) the rate of rotation of the wind axis with respect to the earth axis, sometimes called flow curvature effect. Further, new literal approximations to the longitudinal and lateral-directional modes have been obtained in terms of the redefined dynamic stability parameters. The new approximations, for instance, correctly relate the short-period natural frequency to the longitudinal static stability parameter Cmα.

Photometric determination of rotation axis inclination, rotation rate, and mass of rapidly rotating intermediate-mass stars

Context.Intermediate-mass stars are often fast rotators, and hence are centrifugally flattened and notably affected by gravity darkening. To analyse this kind of stars properly, one must resort to 2D models to compute the visible radiative flux and to take the geometrical effect of the star inclination into account.Aims.Assuming a given stellar age and chemical composition, our aim is to derive the mass and rotation rates of main sequence fast rotating stars, along with their inclination, from photometric quantities influenced by gravity darkening.Methods.We chose three observables that vary with mass, rotation, and inclination: the temperature derived by the infrared flux methodTIRFM, the Strömgrenc1index, and a second indexc2built in the same way as thec1index, but sensitive to the UV side of the Balmer jump. These observables are computed from synthetic spectra produced with the PHOENIX code and rely on a 2D stellar structure from the ESTER code. These quantities are computed for a grid of models in the range 2–7M⊙, and rotation rates from 30% to 80% of the critical rate. Then, for any triplet (TIRFM,c1,c2), we try to retrieve the mass, rotation rate, and inclination using a Levenberg-Marquardt scheme, after a selection step to find the most suitable starting models.Results.Hare-and-hound tests showed that our algorithm can recover the mass, rotation rate, and inclination with a good accuracy. The difference between input and retrieved parameters is negligible for models lying on the grid and is less than a few percent otherwise. An application to the real case of Vega showed that theufilter is located in a spectral region where the modelled and observed spectra are discrepant, and led us to define a new filter. Using this new filter and subsequent index, the Vega parameters are also retrieved with satisfactory accuracy.Conclusions.This work opens the possibility to determine the fundamental parameters of rapidly rotating early-type stars from photometric space observations.

Evaluation of Temporomandibular Joint in Patients with Parkinson's Disease: A Comparative Study.

(1) The aim of this study was to perform an evaluation of the temporomandibular joint (TMJ) in patients with Parkinson's disease (PD) and present the morphological differences of the TMJ between healthy subjects and patients with PD. (2) A total of 102 Caucasian subjects were divided equally into two groups. The study group consisted of patients with PD, while the control group comprised healthy subjects. Ten parameters, including anterior joint space (AJS), superior joint space (SJS), posterior joint space (PJS), condyle head length (CHL), condylar neck width (CNW), minor axis of the condyle (MAC), long axis of the condyle (LAC), condylar axis inclination (CI), medial joint space (MJS), and lateral joint space (LJS), were measured using magnetic resonance images. The data were statistically analyzed using paired samples t-test and Student's t-test, with a significance level set at p < 0.05. (3) In the PD group, all TMJ parameters showed a statistically significant difference between both sides of the face (p < 0.05). However, in the control group, AJS, SJS, PJS, CHL, CNW, MAC, CI, MJS, and LJS did not show a statistically significant difference between both sides of the face (p > 0.05), except for LAC (p < 0.05). The asymmetry index values of AJS, SJS, PJS, CHL, CNW, MAC, CI, MJS, and LJS demonstrated a statistically significant difference between the study and control groups (p < 0.05), except for LAC (p > 0.05). (4) Within the limitations of this retrospective study, the findings suggest that TMJ morphology and asymmetry could be associated with PD.

The Correlation of Global Spinal Realignment With the Quality of Life After Corrective Surgery for Delayed Thoracolumbar Osteoporotic Fracture-Related Kyphosis.

Few studies have been conducted to evaluate the precise impact of corrective surgery on sagittal spinal realignment and clinical outcomes in cases of delayed thoracolumbar osteoporotic fracture-related kyphosis. To assess the efficacy of corrective surgery on sagittal spinal alignment and investigate the relationship between spinal alignment and health-related quality of life (HRQoL) in patients with delayed thoracolumbar osteoporotic fracture-related kyphosis. A total of 78 patients were enrolled. The characteristics and surgical variables were meticulously documented. The sagittal spinal parameters were measured, and the HRQoL was evaluated using Oswestry Disability Index (ODI), SF-12 Physical Component Score (SF-12 PCS), and Scoliosis Research Society-22 Patient Questionnaire (SRS-22) before and after surgery. The changes in spinal parameters and HRQoL were analyzed through the paired t -test. The Pearson correlation analysis was performed to analyze the correlation of parameters with HRQoL. Then, a multiple stepwise regression analysis was performed with HRQoL scores as the dependent variable and spinal parameters as the independent variable. The operative time was 185.9 ± 33.2 min, and the estimated blood loss was 782.8 ± 145.2 mL. The results of the paired t -test revealed a significant difference preoperatively and at the final follow-up in the thoracic kyphosis, thoracolumbar kyphosis (TLK), lumbar lordosis, T9 tilt, pelvic tilt, sacral slope, sagittal vertical axis, and spinosacral angle as well as the ODI, SF-12 PCS, and SRS-22 ( P < .05). Multiple stepwise regression analysis revealed that TLK and pelvic tilt, TLK and sagittal vertical axis, and TLK were the primary parameters affecting the ODI, SF-12 PCS, and SRS-22, respectively. Corrective surgery can effectively realign the global spine and improve HRQoL in patients with delayed thoracolumbar osteoporotic fracture-related kyphosis. The change of TLK is a driving factor to realign the global spine.

Pelvic compensation accompanying spinal malalignment and back pain-related factors in a general population: the Wakayama spine study

Some older adults with spinal deformity maintain standing posture via pelvic compensation when their center of gravity moves forward. Therefore, evaluations of global alignment should include both pelvic tilt (PT) and seventh cervical vertebra-sagittal vertical axis (C7-SVA). Here, we evaluate standing postures of older adults using C7-SVA with PT and investigate factors related to postural abnormality. This cross-sectional study used an established population-based cohort in Japan wherein 1121 participants underwent sagittal whole-spine radiography in a standing position and bioelectrical impedance analysis for muscle mass measurements. Presence of low back pain (LBP), visual analog scale (VAS) of LBP, and LBP-related disability (Oswestry Disability Index [ODI]) were evaluated. Based on the PT and C7-SVA, the participants were divided into four groups: normal, compensated, non-compensated, and decompensated. We defined the latter three categories as “malalignment” and examined group characteristics and factors. There were significant differences in ODI%, VAS and prevalence of LBP, and sarcopenia among the four groups, although these were non-significant between non-compensated and decompensated groups on stratified analysis. Moreover, the decompensated group was significantly associated with sarcopenia. Individuals with pelvic compensation are at increased risk for LBP and related disorders even with the C7-SVA maintained within normal range.

Analytical modeling of an inclined folded-beam spring used in micromechanical resonator devices

Accurate estimation of the mechanical behavior of springs is crucial for the proper design of Microelectormechanical systems (MEMS). The main objective of this study is to derive a closed-form equation for the calculation of the stiffness of an inclined spring in the form of folded-beamss. The energy-based method was used to calculate the displacements of a folded-beams that was fixed at one end and giuded at the other end. The analytical model was then compared with the finite element method using ANSYS for different inclination angles of the folded-beams spring, showing good agreement. The angle on inclination has changed from zero to 180 degress, and stiffness of folded-beams is detemined. The derived expressions of the compliances were checked for the case of serpentine springs with inclination angle of zero, and different length ratios against the literature. It is found that neglecting small lengths for calculating the stiffness of the folded-beams spring is not justified. The influential geometrical parameters, including different lengths of the spring and inclination angle of the spring, on the stiffness are studied. It is found that the angle of inclination of the principal axes of spring constants depends on the geometrical parameters, and the angle of inclination has more effect on the stiffness of a folded-beams spring than the number of folds.

On the variability of grain boundary mobility in the isoconfigurational ensemble

Recent grain growth experiments have revealed that the same type of grain boundary can have very different mobilities depending on its local microstructure. In this work, we use molecular dynamics simulations to quantify uncertainty in the reduced mobility of curved grain boundaries for different types of boundary conditions and over a range of initial velocity seeds. We consider cylindrical island grains in Ni with a [001] tilt axis as a model system. Unexpectedly, we find large variation in the reduced mobility of curved grain boundaries depending on the imposed constraints, the initial velocity distribution and grain size. We perform a dynamic propensity analysis inspired by studies of glass forming liquids to analyze sources of variation in reduced mobility. Our work highlights the significant impact of initial velocity distributions on grain boundary motion which has not been analyzed in prior work.

Mixing enthalpy near grain boundaries in Fe-Cr alloy: The results of atomistic simulation

Energy characteristics of symmetric tilt (twin) grain boundaries (GBs) Σ5(210) and Σ5(310) with the tilt axis [001] and boundaries Σ3(111) and Σ3(112) with the tilt axis [11¯0] in a bcc random binary FeCr alloy have been studied using atomistic simulation. The simulation has been carried out based on DFT calculations and two-band semi-empirical potential. We have proposed the formula for calculating the mixing enthalpy near GBs. The relationship between the mixing enthalpy and the energy of the boundary in the alloy has been revealed. Both simulation methods have shown a decrease in the mixing enthalpy near a GB compared to the ideal crystal. Moreover, DFT has predicted a stronger decrease in the mixing enthalpy compared to estimates based on semi-empirical interaction. Based on the obtained dependences of the mixing enthalpy on the alloy composition, phase diagrams for the considered GB regions have been constructed. It has been shown that the GB region is characterized by a higher equilibrium concentration of chromium, and the precipitates of the α'-phase have a lower concentration of chromium compared to the bulk. The smallest difference in equilibrium compositions has been observed for the Σ5(310) and Σ3(112) boundaries, and the largest one for the Σ3(111) boundary, which has the highest energy among considered GBs.

Three-Dimensional Characterization of Aortic Root Motion by Vascular Deformation Mapping

The aorta is in constant motion due to the combination of cyclic loading and unloading with its mechanical coupling to the contractile left ventricle (LV) myocardium. This aortic root motion has been proposed as a marker for aortic disease progression. Aortic root motion extraction techniques have been mostly based on 2D image analysis and have thus lacked a rigorous description of the different components of aortic root motion (e.g., axial versus in-plane). In this study, we utilized a novel technique termed vascular deformation mapping (VDM(D)) to extract 3D aortic root motion from dynamic computed tomography angiography images. Aortic root displacement (axial and in-plane), area ratio and distensibility, axial tilt, aortic rotation, and LV/Ao angles were extracted and compared for four different subject groups: non-aneurysmal, TAA, Marfan, and repair. The repair group showed smaller aortic root displacement, aortic rotation, and distensibility than the other groups. The repair group was also the only group that showed a larger relative in-plane displacement than relative axial displacement. The Marfan group showed the largest heterogeneity in aortic root displacement, distensibility, and age. The non-aneurysmal group showed a negative correlation between age and distensibility, consistent with previous studies. Our results revealed a strong positive correlation between LV/Ao angle and relative axial displacement and a strong negative correlation between LV/Ao angle and relative in-plane displacement. VDM(D)-derived 3D aortic root motion can be used in future studies to define improved boundary conditions for aortic wall stress analysis.

Relationship between sacral‐abdominal wall distance and grip strength in postmenopausal osteoporotic patients

AbstractBackgroundAn increase in waist circumference (WC) is a factor in lifestyle‐related diseases. The rectus abdominis muscle is a skeletal muscle that attaches to the pelvis from the xiphoid process and is thought to be affected by kyphosis deformity and posterior pelvic tilt. The purpose of this study is to examine differences between sacral‐abdominal wall distance (SAD) and WC and to determine whether they are associated with fall risk, frailty, markers of sarcopenia (grip strength and lean body mass), and spinal alignment. A secondary objective is to examine these differences by stratification by grip strength.MethodsThis retrospective study included 239 women aged 65 years or older (mean age 76.5 ± 6.7 years) attending an outpatient osteoporosis clinic. Bone mineral density and skeletal body composition (muscle mass index and trunk lean mass) were measured using dual‐energy X‐ray absorptiometry. SAD, pelvic tilt, and sagittal longitudinal axis were measured from simple X‐ray images of the spine sides. WC, grip strength, frailty, and fall risk score were investigated. Statistics were performed using Stat Flex, with two‐sided P &lt; 0.05 being significantly different.ResultsWC was correlated with SAD (R = 0.68, P &lt; 0.001). The SAD cut‐off value for a WC of 90 cm was 167 mm. The relationship between grip strength, SAD, and WC, weaker grip strength was associated with greater SAD; however, no significant difference was noted in WC. WC was not correlated with pelvic alignment but was correlated with body mass index (P &lt; 0.01). Meanwhile, SAD was correlated with body mass index, pelvic tilt, sagittal longitudinal axis (P &lt; 0.01), spinal alignment, and WC. Logistic regression analysis was performed with a grip strength of less than 18 kg as the objective variable. We found that the conditions for a grip strength of less than 18 kg were older age (P &lt; 0.001), increased SAD (P = 0.02), and decreased trunk lean body mass. There was a decrease in grip strength (P &lt; 0.05) and an increase in frailty (P &lt; 0.05) and falls (P &lt; 0.01) score in patients with SAD of 167 mm or greater.ConclusionsSAD and WC were found to be correlated; SAD was associated with body weight, posterior pelvic tilt, and anterior spinal tilt deformity, while WC was related to body weight. Increased SAD was found to be linked with decreased grip strength and increased risk of falls. This study was the first to examine a new measurement, SAD, for its utility in assessing grip strength, spinal alignment, frailty, and fall risk.

Poster 269: 4-in-1 Quadricepsplasty for Habitual and Fixed Lateral Patellar Dislocation in Children

Poster 269: 4-in-1 Quadricepsplasty for Habitual and Fixed Lateral Patellar Dislocation in Children

The identification of possible reference planes on a CBCT scan taken with a small FOV—an observational analytical study

Abstract Objectives Unlike a CBCT scan which has a large field of view (FOV), a scan with a small FOV may not involve the base of the skull. Therefore, routinely used reference planes may not be available to evaluate treatment outcome. The present study was undertaken to determine if the palatal plane and a molar occlusal plane may be used as reference planes to measure the change in the axial inclination of the maxillary central incisor and the maxillary first permanent molar towards the end of orthodontic treatment on a CBCT scan captured with a small FOV. Materials and methods A lateral cephalogram and a CBCT scan with a small FOV were taken for fifteen young adults prior to, and six months after, mini-implant supported, distal movement of the maxillary arch. CBCT multi-planar slices were sequentially viewed to obtain an image that contained the entire length of the maxillary central incisor and the maxillary first permanent molar in the tangential view. The axial inclination of the maxillary central incisor and the maxillary first permanent molar was measured from the palatal plane and the molar occlusal plane on both sides. The same parameters were evaluated on the lateral cephalogram using the palatal plane as a reference. An independent t test (p = 0.05) was conducted to compare the results. A Bland–Altman plot with linear regression was constructed to measure accuracy, method agreement and reliability. Results There was no statistically significant difference when a change in the axial inclination of the maxillary central incisor and the maxillary first permanent molar was measured using the two reference planes. The change in axial inclination of the maxillary central incisor and maxillary first permanent molar had a 95% confidence interval of -1.82 to 4.19 and -4.48 to 3.05 and a p-value of 0.425 and 0.701 on the right side, respectively, and a 95% confidence interval of -1.76 to 4.79 and -4.41 to 2.79 and p-value of 0.350 and 0.650 on the left side. Conclusions The molar occlusal plane and the palatal plane may be used as reference planes for measuring change in the axial inclination of the maxillary central incisor and the first permanent molar in a CBCT scan taken with a small FOV.

Application of the OPG in the Prediction of Unfavorably Angulated Canines: An Original Study.

Achieving a correct occlusion depends heavily on the axial inclination of the teeth, particularly the maxillary anteriors, which have the longest crowns. This study, which expanded the use of angular measures to the mandible, was created to determine the prevalence of adversely angulated canines using orthopantomograms. A sample of 200 people between the ages of 18 and 25 was chosen and separated into two groups based on the degree of crowding; one group served as the control group while the other, which experienced severe, crowding, served as the study group. All of the individuals had their Orthopantomogram and study models taken. While canine angulation in controls typically ranges from 85 to 95 degrees, cases of crowding were observed to have angulation as low as 67 degrees and as high as 105 degrees. Orthopantomogram can be used to predict canine angulation, with distally and mesially angulated canines occurring at rates of roughly 18% and 37%, respectively.

Gullies on Mars could have formed by melting of water ice during periods of high obliquity.

Gullies on Mars resemble water-carved channels on Earth, but they are mostly at elevations where liquid water is not expected under current climate conditions. It has been suggested that sublimation of carbon dioxide ice alone could have formed Martian gullies. We used a general circulation model to show that the highest-elevation Martian gullies coincide with the boundary of terrain that experienced pressures above the triple point of water when Mars' rotational axis tilt reached 35°. Those conditions have occurred repeatedly over the past several million years, most recently ~630,000 years ago. Surface water ice, if present at these locations, could have melted when temperatures rose >273 kelvin. We propose a dual gully formation scenario that is driven by melting of water ice followed by carbon dioxide ice sublimation.

X-ray polarimetry of X-ray pulsar X Persei: another orthogonal rotator?

ABSTRACT X Persei is a persistent low-luminosity X-ray pulsar of period of ≈ 835 s in a Be binary system. The field strength at the neutron star surface is not known precisely, but indirect signs indicate a magnetic field above 1013 G, which makes the object one of the most magnetized known X-ray pulsars. Here we present the results of observations X Persei performed with the Imaging X-ray Polarimetry Explorer (IXPE). The X-ray polarization signal was found to be strongly dependent on the spin phase of the pulsar. The energy-averaged polarization degree in 3–8 keV band varied from several to ∼20 per cent over the pulse with a phase dependence resembling the pulse profile. The polarization angle shows significant variation and makes two complete revolutions during the pulse period, resulting in nearly nil pulse-phase averaged polarization. Applying the rotating vector model to the IXPE data we obtain the estimates for the rotation axis inclination and its position angle on the sky, as well as for the magnetic obliquity. The derived inclination is close to the orbital inclination, reported earlier for X Persei. The polarimetric data imply a large angle between the rotation and magnetic dipole axes, which is similar to the result reported recently for the X-ray pulsar GRO J1008−57. After eliminating the effect of polarization angle rotation over the pulsar phase using the best-fitting rotating vector model, the strong dependence of the polarization degree with energy was discovered, with its value increasing from 0 at ∼2 keV to 30per cent at 8 keV.