Axial Asymmetry Research Articles

SPIN-ORBIT COUPLING AND CHAOTIC ROTATION FOR COORBITAL BODIES IN QUASI-CIRCULAR ORBITS

Coorbital bodies are observed around the Sun sharing their orbits with the planets, but also in some pairs of satellites around Saturn. The existence of coorbital planets around other stars has also been proposed. For close-in planets and satellites, the rotation slowly evolves due to dissipative tidal effects until some kind of equilibrium is reached. When the orbits are nearly circular, the rotation period is believed to always end synchronous with the orbital period. Here we demonstrate that for coorbital bodies in quasi-circular orbits, stable non-synchronous rotation is possible for a wide range of mass ratios and body shapes. We show the existence of an entirely new family of spin-orbit resonances at the frequencies $n\pm k\nu/2$, where $n$ is the orbital mean motion, $\nu$ the orbital libration frequency, and $k$ an integer. In addition, when the natural rotational libration frequency due to the axial asymmetry, $\sigma$, has the same magnitude as $\nu$, the rotation becomes chaotic. Saturn coorbital satellites are synchronous since $\nu\ll\sigma$, but coorbital exoplanets may present non-synchronous or chaotic rotation. Our results prove that the spin dynamics of a body cannot be dissociated from its orbital environment. We further anticipate that a similar mechanism may affect the rotation of bodies in any mean-motion resonance.

All biometric components are important in anisometropia, not just axial length

BackgroundNo study to date has looked into the relationship between ocular biometrics with anisometropia exclusively; therefore, the purpose of this study was to determine the relationship between anisometropia and ocular...

An experimental study of the natural noise in the Transit-M hypersonic wind tunnel

Tests were performed at Mach number M = 6. Observations of flow pulsations were performed with the help of high-frequency measurements of pressure and heat fluxes and with the help of hot-wire anemometry. Measurements were carried out in a broad range of Re1 numbers at various orientations and locations of sensors with respect to the nozzle exit plane. It is shown that the Transit-M noise varies weakly over the longitudinal coordinate, whereas on moving along the radial coordinate, some increase of the fluctuation level is observed due to approaching the mixing layer. Also, the distribution of axial asymmetry of the noise level was obtained.

Improved asymmetric peak parameter refinement

New expressions for the calculation of axial asymmetry peak shape parameter derivatives in the Finger, Cox and Jephcoat model [J. Appl. Cryst. (1994), 27, 892–900] are presented. Code utilizing the new expressions shows an improved range of convergence for powder diffraction peak shape refinements, particularly when the parameters are transformed to A = H + S and B = H − S.

Design of a new axially chiral molecule by conformational fixation: 2,6-dithiaspiro[3.3]heptane 2,6-dioxide and its heavier analogues

We have designed a new axially chiral bis(sulfoxide) molecule with conformational rigidity: 2,6-dithiaspiro[3.3]heptane 2,6-dioxide 2a. This molecule has axial asymmetry due to two puckered thietane ring systems. The lone pairs on the sulfur show a strong s-character, which was expected to result in a high barrier to racemization, that is, inversion at the sulfur. We confirmed this prediction by calculations and experimentation. The lone pairs of the sulfur in 2a are sp1.00 and the enthalpy of activation (ΔH‡) for inversion is 47.5kcal/mol (B3LYP/6-31G(d)). The 1H NMR spectra of 2a showed two doublets and two doubled doublet peaks, which resulted from the rigidity of the four-membered ring frameworks without flipping. We separated the enantiomers of 2a by HPLC with a chiral stationary phase column to observe a set of complementary peaks. We also calculated the diselena- and ditellura congeners and confirmed that they also show axial chirality.

Mode transformation using graded photonic crystals with axial asymmetry

We propose a mode conversion method that enables transformation of the propagating mode from fundamental to higher-order modes by utilizing asymmetric graded index (A-GRIN) structures. Refractive index variations of two different asymmetric gradient profiles, i.e., exponential and Luneburg lens profiles, have been approximated by two-dimensional photonic crystals (PCs). The basic structure is composed of constant radii with different lattice sizes. The designed GRIN mode converters provide relatively high transmission efficiency in the spectral region of interest and achieve the transformation in compact configuration. Numerical approaches utilizing the finite-difference time-domain and plane wave expansion methods are used to analyze the mode conversion phenomenon of proposed GRIN PC media. Analytical formulation based on ray theory is outlined to explore both ray trajectories and the physical concept of a wavefront retardation mechanism.

Axial asymmetry in the IVBM

The dynamical symmetry limit of the two-fluid Interacting Vector Boson Model (IVBM), defined through the chain $Sp(12,R) \supset U(3,3) \supset U_{p}(3) \otimes \overline{U_{n}(3)} \supset SU^{\ast}(3) \supset SO(3)$, is considered and applied for the description of nuclear collective spectra exhibiting axially asymmetric features. The effect of the introduction of a Majorana interaction to the $SU^{\ast}(3)$ model Hamiltonian on the $\gamma$-band energies is studied. The theoretical predictions are compared with the experimental data for $^{192}Os$, $^{190}Os$, and $^{112}Ru$ isotopes. It is shown that by taking into account the full symplectic structures in the considered dynamical symmetry of the IVBM, the proper description of the energy spectra and the $\gamma$-band energy staggering of the nuclei under considerations can be achieved. The obtained results show that the potential energy surfaces for the following two nuclei $^{192}Os$ and $^{112}Ru$, possess almost $\gamma$-flat potentials with very shallow triaxial minima, suggesting a more complex and intermediate situation between $\gamma$-rigid and $\gamma$-unstable structures. Additionally, the absolute $B(E2)$ intraband transition probabilities between the states of the ground state band and $\gamma$ band, as well as the $B(M1)$ interband transition probabilities between the states of the ground and $\gamma$ bands for the two nuclei $^{192}Os$ and $^{190}Os$ are calculated and compared with experiment and for the $B(E2)$ values with the predictions of some other collective models incorporating the $\gamma$-rigid or $\gamma$-unstable structures. The obtained results agree well with the experimental data and reveal the relevance of the used dynamical symmetry of IVBM in the description of nuclei exhibiting axially asymmetric features in their spectra.

African Descent and Glaucoma Evaluation Study

The purpose of the study is to determine the degree of intereye asymmetry of optic disc topography and retinal nerve fiber layer (RNFL) thickness in healthy individuals of African descent (AD) and European descent (ED). Observational, clinical study. Five hundred nineteen healthy individuals (AD, n=262, mean age=44.9 years; ED, n=257, mean age=47.1 years) from the African Descent and Glaucoma Evaluation Study and Diagnostic Innovations in Glaucoma Study were tested using Heidelberg retina romograph (HRT), GDx variable corneal compensation (GDx-VCC), and standard, automated perimetry within 6 months of one another. HRT-II measurements included cup area, cup volume, rim area, and rim volume. GDx-VCC measurements included average RNFL thickness. Intereye asymmetry was calculated as the absolute value of the differences in measurements between the right and left eye. AD participants showed significantly higher median asymmetry in cup volume and rim volume (P<0.001 and 0.033, respectively) compared with ED participants. The effect of race lost significance after adjustment for mean disc area and disc area asymmetry in multivariable models. Axial length asymmetry was not correlated with increased asymmetry in any of this study's asymmetry parameters. Normal ranges of asymmetry for the HRT-II measurements of cup area (up to 0.39 mm), cup volume (up to 0.15 mm), rim area (up to 0.45 mm), and rim volume (up to 0.22 mm) were derived, as were asymmetry ranges for GDx-VCC-measured average RNFL thickness (up to 6.25 μm). The effect of race was no longer significant after adjustment for mean disc area and disc area asymmetry. Individuals with asymmetries with magnitudes greater than those of the normal ranges could be considered as suspicious for glaucoma.

Design of a new axially chiral molecule by conformational fixation: 2,6-diphospha- and 2,6-diarsaspiro[3.3]heptanes

We have designed a new axially chiral diphosphine that shows conformational rigidity: 2,6-diphosphaspiro[3.3]heptane 2a. This molecule has axial asymmetry due to puckering of the two phosphetane ring systems. Although its nitrogen congener 2,6-diazaspiro[3.3]heptane 1a is easily racemized, 2,6-diphosphaspiro[3.3]heptane 2a does not racemize at ambient temperature because the lone pairs on the phosphorus atoms have a strong s-character, which results in a high barrier to inversion at the phosphorus, that is, a high barrier to racemization. We also calculated the properties of the diarsa congener 3a and predicted that it also exhibits axial chirality and that it can be separated into enantiomers at ambient temperature.

Profile of Anisometropia and Aniso-Astigmatism in Children: Prevalence and Association with Age, Ocular Biometric Measures, and Refractive Status

We describe the profile and associations of anisometropia and aniso-astigmatism in a population-based sample of children. The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit a representative sample of children from schools in Northern Ireland. Examinations included cycloplegic (1% cyclopentolate) autorefraction, and measures of axial length, anterior chamber depth, and corneal curvature. χ(2) tests were used to assess variations in the prevalence of anisometropia and aniso-astigmatism by age group, with logistic regression used to compare odds of anisometropia and aniso-astigmatism with refractive status (myopia, emmetropia, hyperopia). The Mann-Whitney U test was used to examine interocular differences in ocular biometry. Data from 661 white children aged 12 to 13 years (50.5% male) and 389 white children aged 6 to 7 years (49.6% male) are presented. The prevalence of anisometropia ≥1 diopters sphere (DS) did not differ statistically significantly between 6- to 7-year-old (8.5%; 95% confidence interval [CI], 3.9-13.1) and 12- to 13-year-old (9.4%; 95% CI, 5.9-12.9) children. The prevalence of aniso-astigmatism ≥1 diopters cylinder (DC) did not vary statistically significantly between 6- to 7-year-old (7.7%; 95% CI, 4.3-11.2) and 12- to 13-year-old (5.6%; 95% CI, 0.5-8.1) children. Anisometropia and aniso-astigmatism were more common in 12- to 13-year-old children with hyperopia ≥+2 DS. Anisometropic eyes had greater axial length asymmetry than nonanisometropic eyes. Aniso-astigmatic eyes were more asymmetric in axial length and corneal astigmatism than eyes without aniso-astigmatism. In this population, there is a high prevalence of axial anisometropia and corneal/axial aniso-astigmatism, associated with hyperopia, but whether these relations are causal is unclear. Further work is required to clarify the developmental mechanism behind these associations.

Finite Element Analysis of Material Flow in Mechanical Clinching with Extensible Dies

An investigation of the material flow during the clinching process with extensible dies is carried out. Clinched joints were produced under different forming loads to evaluate the evolution of the jointsprofile experimentally. Tensile-shear tests were conducted to evaluate the influence of the forming load on mechanical strength of the clinched joint. Since the jointsstrength depends on the jointsprofile, which in turn depends on the punch-die cavity volume, an analysis of the forces acting on the extensible dies was carried out. A finite element model was developed and validated by comparing the predicted and measured material flow and quality criteria (e.g., neck thickness and undercut). Therefore, the FE model was utilized to analyze the evolution of contact forces acting on the die sectors during the joining process. Furthermore, the main causes of the asymmetry in the cross section of such joints have been studied. It turned out that the axial asymmetry due to material flow within the gap between consecutive die sectors increases with the punch force and the sheet thickness.

Effect of blade outlet angle on radial thrust of single-blade centrifugal pump

Single-blade centrifugal pumps are widely used as sewage pumps. However, a large radial thrust acts on a single blade during pump operation because of the geometrical axial asymmetry of the impeller. This radial thrust causes vibrations of the pump shaft, reducing the service life of bearings and shaft seal devices. Therefore, to ensure pump reliability, it is necessary to quantitatively understand the radial thrust and clarify the behavior and generation mechanism. This study investigated the radial thrust acting on two kinds of single-blade centrifugal impellers having different blade outlet angles by experiments and computational fluid dynamics (CFD) analysis. Furthermore, the radial thrust was modeled by a combination of three components, inertia, momentum, and pressure, by applying an unsteady conservation of momentum to this impeller. As a result, the effects of the blade outlet angle on both the radial thrust and the modeled components were clarified. The total head of the impeller with a blade outlet angle of 16 degrees increases more than the impeller with a blade outlet angle of 8 degrees at a large flow rate. In this case, since the static pressure of the circumference of the impeller increases uniformly, the time-averaged value of the radial thrust of both impellers does not change at every flow rate. On the other hand, since the impeller blade loading becomes large, the fluctuation component of the radial thrust of the impeller with the blade outlet angle of 16 degrees increases. If the blade outlet angle increases, the fluctuation component of the inertia component will increase, but the time-averaged value of the inertia component is located near the origin despite changes in the flow rate. The fluctuation component of the momentum component becomes large at all flow rates. Furthermore, although the time-averaged value of the pressure component is almost constant, the fluctuation component of the pressure component becomes large at a large flow rate. In addition to the increase of the fluctuation component of this pressure component, because the fluctuation component of the inertia and momentum components becomes large (as mentioned above), the radial thrust increases at a large flow rate, as is the case for the impeller with a large blade outlet angle.

Cyclic powder formation during pulsed injection of hexamethyldisiloxane in an axially asymmetric radiofrequency argon discharge

A new approach of periodic production of dusty plasma consisting of pulsed injection of hexamethyldisiloxane (HMDSO) in argon axially asymmetric radiofrequency (RF) discharge was investigated in this work. The range of plasma operating conditions in which this dusty plasma can exist was closely examined. The obtained results clearly show that a net periodicity in the formation/disappearance of dust particles in the plasma can be maintained on a very large scale of discharge duration. The significance of discharge axial asymmetry to the dust particles behaviour in the plasma is revealed by the development of an asymmetric in shape void shifted towards the powered RF electrode. The key role of the reactive gas and its pulsed injection on each stage of the oscillating process of formation/disappearance of dust particles is disclosed by optical and electrical measurements. It is shown that the period of dusty plasma formation/disappearance is inversely related to the HMDSO injection time. Moreover, the impact of time injection over short period (5 s) is examined. It indicates the conflicting role played by the HMDSO on the reduction of dusty plasma during the reactive gas injection and the reappearance of particles in the plasma during the time off. The electronegative behavior of the plasma in the presence of negatively charged particles seems to explain the energetic modifications in the discharge. A frequency analysis of the floating potential reveals all these cyclic processes. Particularly, in the 10–200 Hz frequency range, the presence and the evolution of dust particles in the plasma over one generation can be observed.

Characterization and Experimental Verification of the Axial Unbalanced Magnetic Force in Brushless DC Motors

The characteristics of the axial unbalanced magnetic force (UMF) in brushless dc (BLDC) motors were numerically and experimentally investigated. Three-dimensional finite element analysis was conducted to characterize the axial UMF. An experimental device was also developed to measure the axial UMF and verify the simulated results. The axial asymmetry of the permanent magnet (PM) with respect to the stator was found to be a major source of the axial UMF, whose driving frequencies are the least common multiples of the pole and slot. Additional uneven magnetization of the PM and rotor eccentricity introduce slot harmonics to the axial UMF, while additional stator eccentricity generates fundamental and pole harmonics.

Instability of a general rotating system with small axial asymmetry and damping

The paper presents new results on instability of general rotating systems with small axial asymmetry and damping. Rotating systems with arbitrary finite degrees of freedom are considered. Instability conditions are derived for nonresonant and resonant rotation speeds characterized by simple and double eigenvalues. As an application, the stability problem of a rotating elastic shaft with small internal and external damping forces and asymmetric imperfections is studied. The numerical example shows validity and accuracy of the derived analytical formulae for the instability regions.

Development of axial asymmetry in the neutron-rich isotope 110Mo

The neutron-rich nucleus 110Mo has been investigated by means of γ-ray spectroscopy following the β-decay of 110Nb, produced using in-flight fission of a 238U beam at 345 MeV/nucleon at the RIBF facility. In addition to the ground-band members reported previously, spectroscopic information on the low-lying levels of the quasi-γ band built on the second 2+ state at 494 keV has been obtained for the first time. The experimental finding of the second 2+ state being lower than the yrast 4+ level suggests that axially-asymmetric γ softness is substantially enhanced in this nucleus. The experimental results are compared with model calculations based on the general Bohr Hamiltonian method. The systematics of the low-lying levels in even-even A ≈ 110 nuclei is discussed in comparison with that in the neutron-rich A ≈ 190 region, by introducing the quantity Es/E(2+1), Es = E(2+2) − E(4+1) as a global signature of the structural evolution involving axial asymmetry.

Prescribed nondegenerate high-order modes in an axial-asymmetric high-finesse Fabry–Perot microcavity

We report an axial-asymmetric high-Q Fabry-Perot cavity supporting nondegenerate Hermite-Gaussian modes of the same mode order. Axial asymmetry of mirror surface was introduced by mechanically grinding off one side of a cylindrical mirror substrate without degrading the original mirror quality. The bases of the resulting Hermite-Gaussian modes were aligned with respect to the direction of grinding, making it possible to prescribe the mirror principal axes.

Nonlocality of microwave-induced variations in the intensity of the visible continuum from a medium-pressure cesium-xenon dc discharge

A violation of the local relation between the visible continuum (VC) emissivity and the millimeter wave (MMW) intensity was observed in the experiments on imaging of MMW beams with subcentimeter width using the VC from a slab of the positive column (PC) of a medium-pressure cesium-xenon (Cs-Xe) dc discharge. The spatial distribution of the microwave-induced variation in the VC emissivity of the plasma slab was modeled. For this, perturbations of the electron temperature and density in a slab of the PC of a Cs-Xe discharge affected by an MMW beam were calculated. The relation between the spatial distributions of the VC brightness perturbation and the MMW intensity has been obtained. Good agreement between the results of the experiments and the modeling is demonstrated. The line spread function of a two-dimensional (2D) plasma sensor for MMWs is found, and its width is shown to be equal to 2 mm. We proved that the nonlocality of microwave-induced variations in the intensity of the VC from the PC, as well as the spatial resolution of the plasma technique of MMW imaging, are primarily determined by the influence of the electron heat conduction. Along with the electron heat conduction, the nonlocality of the electron temperature variation is caused by the influence of the hydrodynamic flux of electron enthalpy, diffusion and thermodiffusion fluxes of electrons, and also spatial inhomogeneity of the electron heating by a dc electric field, which results from a microwave-induced variation in plasma conductivity. These factors are responsible for the axial asymmetry of the images of the axisymmetric MMW beams.

Characteristics of core refractive index axial asymmetry LPFGs written by femtosecond laser

Direct writing of long period fibre gratings (LPFGs) in standard single mode fibres (SMF) with infrared femtosecond laser pulses is experimentally investigated. It is found that the transmission spectra of LPFGs can be controlled by infrared femtosecond laser focus condition. The transmission spectra of LPFGs present single resonance peak when the microscopic objective is 25´, which is distinct from the LPFGs manufactured by UV laser irradiation with mask. However, when the microscopic objective is 10´, the LPFGs transmission spectra with four rejection bands can be obtained. When the distribution of femtosecond laser energy is changed by inserting a diaphragm, the LPFGs transmission spectra present multi resonance peaks.

Radial Thrust of Single-Blade Centrifugal Pump

Single-blade centrifugal pumps are widely used as sewage pumps. However, the impeller of a single-blade pump is subjected to strong radial thrust during pump operation because of the geometrical axial asymmetry of the impeller. Therefore, to improve pump reliability, it is necessary to quantitatively understand radial thrust and elucidate the behavior and mechanism of thrust generating. This study investigates the radial thrust acting up on a single-blade centrifugal impeller by conducting experiments and CFD analysis. The results show that the fluctuating component of radial thrust increases as the flow rate deviates from the design flow rate to low or high value. Radial thrust was modeled by a combination of three components, inertia, momentum, and pressure by applying an unsteady conservation of momentum to the impeller. The sum of these components agrees with the radial thrust calculated by integrating the pressure and the shearing stress on the impeller surface. The behavior of each component was shown, and the effects of each component on radial thrust were clarified. The pressure component has the greatest effect on the time-averaged value and the fluctuating component of radial thrust. The time-averaged value of the inertia component is nearly 0, irrespective of the change in the flow rate. However, its fluctuating component has a magnitude nearly comparable with the pressure component at a low flow rate and slightly decreased with the increase in flow rate.