Symmetry Force Research Articles

Design and control of a disk-type integrated motor-bearing system

A disk-type integrated motor-bearing system having axial magnetic flux is newly invented and its design, analysis, and control methods are presented. Sinusoidal motoring currents to four symmetrically placed winding groups produce a torque, whereas control currents of the same magnitude but opposite signs added to the opposite winding groups create radial forces. The control currents are intended to break force symmetry, resulting in unbalanced radial forces. The system employs two stators not only to effectively remove the rotational frequency modulation effect in the radial control forces, but also to reduce the torque ripple. It is shown that the prototype integrated motor-bearing system built in the laboratory succeeds in stable radial direction control and operation of the rotor.

Vibrational Analysis of Ferrocyanide Complex Ion Based on Density Functional Force Field

Vibrational properties of ferrocyanide complex ion, <TEX>$[Fe(CN)_6]^{4-}$</TEX> , have been studied based on the force constants obtained from the density functional calculations at B3LYP/<TEX>$6-31G^{\ast\ast}$</TEX> level by means of the normal mode analysis using new bond angle and linear angle internal coordinates recently developed. Vibrations of ferrocyanide were manipulated by twenty-three symmetry force constants. The angled bending deformations of C-Fe-C, the linear bending deformations of Fe-C<TEX>${\equiv}$</TEX>N and the stretching vibrations of Fe-C have been quantitatively assigned to the calculated frequencies. The force constants in the internal coordinates employed in the modified Urey-Bradley type potential were evaluated on the density functional force field applied, and better interaction force constants in the internal coordinates have been proposed. The valence force constants in the general quadratic valence force field were also given. The stretch-stretch interaction and stretch-bending interaction constants are not sensitive to the geometrical displacement in the valence force field.

Symmetry-adapted perturbation theory with regularized Coulomb potential

We present a novel formulation of the symmetry-adapted perturbation theory involving a regularization of the Coulomb singularities in the interaction operator. The perturbation development is performed in two stages. At the first stage, we apply the weak symmetry forcing to a regularized interaction operator and, subsequently, at the second stage we treat the singular, short-range part of the perturbation by employing the strong symmetry forcing characteristic of the Eisenschitz–London–Hirschfelder–van der Avoird theory. The correct asymptotics is recovered at the first stage and the residual, short-range part of the perturbation is sufficiently weakened by the symmetry projection to prevent the divergence of the series appearing at the second stage of our procedure. We tested the method by performing high-order calculations of the interaction energy in the singlet and triplet states resulting from the interaction of two ground-state hydrogen atoms. A large basis set of Gaussian geminals was used to obtain saturated results. It is shown that the proposed regularization procedure eliminates the pathological convergence properties observed earlier for the perturbation expansions involving the weak symmetry forcing and gives very accurate interaction energies in a low-order treatment of the singular part of the potential.

Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

Smoothed Particle Hydrodynamics in cosmology: a comparative study of implementations

We analyse the performance of 12 different implementations of Smoothed Particle Hydrodynamics (SPH) using seven tests designed to isolate key hydrodynamic elements of cosmological simulations which are known to cause the SPH algorithm problems. In order, we consider a shock tube, spherical adiabatic collapse, cooling flow model, drag, a cosmological simulation, rotating cloud-collapse and angular momentum transport. In the implementations special attention is given to the way in which force symmetry is enforced in the equations of motion. We study in detail how the hydrodynamics are affected by different implementations of the artificial viscosity including those with a shear-correction modification. We present an improved first-order smoothing-length update algorithm that is designed to remove instabilities that are present in simple forward prediction algorithms. Gravity is calculated using the adaptive particle–particle, particle–mesh algorithm. For all tests we find that the artificial viscosity is the single most important factor distinguishing the results from the various implementations. The shock tube and adiabatic collapse problems show that the artificial viscosity used in the hydra code prior to version 4.0 performs relatively poorly for simulations involving strong shocks when compared to a more standard artificial viscosity. The shear-correction term is shown to reduce the shock-capturing ability of the algorithm and to lead to a spurious increase in angular momentum in the rotating cloud-collapse problem. For the disc stability test, the shear-corrected and previous hydra artificial viscosities are shown to reduce outward angular momentum transport. The cosmological simulations produce comparatively similar results, with the fraction of gas in the hot and cold phases varying by less than 10 per cent amongst the versions. Similarly, the drag test shows little systematic variation amongst versions. The cooling flow tests show that implementations using the force symmetrization of Thomas & Couchman are more prone to accelerate the overcooling instability of SPH, although the problem is generic to SPH. The second most important factor in code performance is the way force symmetry is achieved in the equation of motion. Most results favour a kernel symmetrization approach. The exact method by which SPH pressure forces are included in the equation of motion appears to have comparatively little effect on the results. Combining the equation of motion presented by Thomas & Couchman with a modification of the Monaghan & Gingold artificial viscosity leads to an SPH scheme that is both fast and reliable.

Discovering mirror particles at the Large Hadron Collider and the implied cold universe

The Mirror Matter or Exact Parity Model sees every standard particle, including the physical neutral Higgs boson, paired with a parity partner. The unbroken parity symmetry forces the mass eigenstate Higgs bosons to be maximal mixtures of the ordinary and mirror Higgs bosons. Each of these mass eigenstates will therefore decay 50% of the time into invisible mirror particles, providing a clear and interesting signature for the Large Hadron Collider (LHC) which could thus establish the existence of the mirror world. However, for this effect to be observable the mass difference between the two eigenstates must be sufficiently large. In this paper, we study cosmological constraints from Big Bang Nucleosynthesis on the mass difference parameter. We find that the temperature of the radiation dominated (RD) phase of the universe should never have exceeded a few 10's of GeV if the mass difference is to be observable at the LHC. Chaotic inflation with very inefficient reheating provides an example of how such a cosmology could arise. We conclude that the LHC could thus discover the mirror world and simultaneously establish an upper bound on the temperature of the RD phase of the universe.

Bicycle Pedal Kinetics Following Force Symmetry Feedback Training in Subjects with Unilateral Cerebrovascular Accident

The purpose of this sludy was to compare individual pedal reaclion force components following bicycle training with and without effective force feedback in subjects with unilateral cerebrovascular accident (CVA). Eight ambulatory subjects with CVA were studied on a recumbent bicycle equipped with custom-built pedals, which measure normal and tangential components of the load applied to the pedal surface. Comparisons of normal and tangential pedal reaction forces were made following 1 month of bicycle training (3 times/week for 4 weeks) during retention tests performed without feedback. The ratios of involved to contralateral (I/C ratios) force parameters were used to assess symmetry. Subjects were randomly assigned to 2 groups: (a) a feedback group that received visual/verbal feedback regarding effective force patterns, bilaterally, after each trial; and (b) a no-feedback group dial received no feedback. Two critical results were found: (a) tangential pedal forces were significantly more posteriorly directed bilaterally following training across all subjects, but the change was greater for the no-feedback group relative to the feedback group, and (b) effective force feedback training did not demonstrate improvements in the I/C ratios above that of the control group. A more posteriorly applied tangential pedal force may represent increased dorsiflexion and may suggest that bicycle training facilitated ankle control. The cyclical nature of cycling, however, may allow for natural patterns to develop without feedback or may require less frequent use of feedback based on retention test performance.

Aquales Funktionstraining als alternatives Behandlungsregime in der Rehabilitation von Patienten mit retropatellaren Kniegelenkschäden

Objective: Assessment of the effectiveness of an aquatic functional training in the rehabilitation of diseases of the retropatellar joint. Subjects: In the frame of a controlled comparative study for evaluation of three kinds of physical treatment the functional adaptations of 45 patients aged from 37 to 52 years were investigated. Design: 11 female and 28 male patients were randomized into three treatment groups. Six male patients formed the control group. The treatment groups carried out an ambulant rehabilitation programme with physical applications four times weekly each time 120 Minutes over a period of 8 weeks. The standard group got the physical applications only. The programme of the land group was supplemented by a muscle training on machines for 60 minutes per therapy unit. The water group carried out additionally an aquatic functional training each time twice 30 minutes. The four groups were tested at the beginning (T1), at the end (T2) and three months after T2 (T3). Stretch ability and strength of the tigh muscles, the reaction forces of the ground while walking and the functional status of the retropatellar joint by means of a clinical score was investigated by the examiner. Results: In T1 was a homogenous level in all groups. While the results of the control group remained virtually unchanged over the period of investigation the standard and the land group got a significant improvement in T2 in all of the parameters investigated and returned in T3 to the level at the beginning. However, in the water group as well the stretch ability and the strength of the tigh muscles as the symmetry of the reaction forces while walking and the functional status of the joint increased in T2 over the level of the other treatment groups. In T3 the status was stabilized and led to decreased trouble in the retropatellar joint. Conclusions: The accomodatic resistance and the physical properties of the medium water induced strengthening of the muscles in a gentle way and an improved function of the arthron. The aquatic functional training does not represent only an alternative kind of treatment, but seems to be the most promising method in the rehabilitation of the diseases of the retropatellar joint. Further investigations have to evaluate long-term effects.

Symmetry Force Fields for Neutral and Ionic Transition Metal Carbonyl Complexes from Density Functional Theory

Symmetry force fields for neutral and ionic transition metal carbonyl complexes have been derived on the basis of gradient-corrected density functional calculations using effective core potential wave functions in conjunction with polarized triple-ζ basis sets. For the neutral carbonyls [M(CO)6] (M = Cr, Mo, W), Fe(CO)5, and Ni(CO)4, the calculated data are compared to experimentally derived force fields. For three different series of transition metal carbonyl ions, trends in the force fields are discussed in terms of bonding models and electrostatic effects, emphasizing the variation of the calculated results with the total charge of the carbonyl complex. The limitations of the empirical Cotton−Kraihanzel approach are analyzed.

CMe 3SiX 3 and SiMe 3SiX 3 (X=H, F, Cl, Br, I): a combined ab initio and vibrational spectroscopic study

The infrared and Raman vibrational spectra of the tert-butylsilanes CMe 3SiX 3 and disilanes SiMe 3SiX 3 (X=H, F, Cl, Br, I) have been measured and assigned with the help of normal coordinate analyses and potential energy distribution analyses employing ab initio optimized geometries and ab initio symmetry force constants. Scaled theoretical SiX and SiSi force constants are smaller than values estimated by extrapolation from spectroscopic force constants of related disilanes. The synthesis of the novel compound SiMe 3SiI 3 and the residual disilanes SiMe 3SiX 3 (X=H, F, Cl, Br) is described.

Chiral symmetry and three-nucleon forces

After a brief review of the role three-nucleon forces play in the few-nucleon systems, the chiral-perturbation-theory approach to these forces is discussed. Construction of the (nominal) leading- and subleading-order Born terms and pion-rescattering graphs contributing to two-pion-exchange three-nucleon forces is reviewed, and comparisons are made of the types of such forces that are used today. It is demonstrated that the short-range {ital c} term of the Tucson-Melbourne force is unnatural in terms of power counting and should be dropped. The class of two-pion-exchange three-nucleon forces then becomes rather uniform. {copyright} {ital 1999} {ital The American Physical Society}

Lyapunov exponent of dilute gas, liquid and solid plasmas

The Lyapunov exponent has been investigated both numerically and analytically for various plasma states. With the use of a three-dimensional particle code that calculates Coulomb forces among individual particles, instantaneous expansion rates of nearby trajectories in a phase space are studied. It is found that the Lyapunov exponent has different dependences on the Coulomb coupling constant corresponding to dilute, liquid and solid plasmas. An analytical model is also developed and it gives a relation between the Lyapunov exponent and the dielectric response function. The model indicates that the Lyapunov exponent is of the order of the plasma frequency in a dilute plasma, which agrees with simulation results. In a dilute plasma, large fluctuation of the instantaneous expansion rate is shown to be caused by a close encounter which breaks the symmetry of force and leads to trajectory instability.

Conformational properties of the methylated disilanes MeX 2SiSiX 2Me (X=H, F, Br and I): a combined ab initio and vibrational spectroscopic study

Together with ab initio calculations, Raman spectra of the methylated disilanes MeX 2SiSiX 2Me (X=H, F, Br and I) unambiguously prove the presence of two rotamers, anti and gauche in the liquid state. Energy differences between rotational isomers have been determined from variable temperature Raman spectra employing Van't Hoff plots of the logarithm of intensity ratios vs. the inverse temperature. For the disilanes with X=F, Br and I the anti conformation is preferred in the liquid state. For MeH 2SiSiH 2Me the gauche rotamer is slightly stabilized by 0.43 kJ mol −1. Vibrational spectra have been assigned by the help of normal coordinate analyses using optimized geometries and ab initio symmetry force fields.

A Mechanism for the Barotropic Equilibration of Baroclinic Waves

Abstract The barotropic instability of finite amplitude waves is suggested as a mechanism for explaining the equilibration of a baroclinic wave growing in a meridionally independent vertical shear flow. A quasigeostrophic two-layer channel model on an f-plane is used to give evidence for this hypothesis. Three solutions with different flow symmetries are adopted for the analysis. Numerical simulations reveal that the flow symmetry of the initial small amplitude perturbation can have a large impact on wave structure evolution and energetics. The flow symmetry of the first solution forces the wave to excite symmetric life cycles with baroclinic growth and baroclinic decay. The flow symmetries of the other solutions enable the wave to undergo an asymmetric life cycle with baroclinic growth followed by a barotropic decay that occurs when the fundamental wave has a sufficiently large aspect ratio. Accordingly, a linear-stability analysis of a steady barotropic wave reveals an increasing destabilization with in...

Vibrational Spectra and Normal Coordinate Analysis of Diamminediiodidezinc(II) with 15N and 2H Isotopic Substitution.

The Raman and IR. spectra of solid diamminediiodidezinc (II) with 15N and 2H isotopic substitution have been measured. The spectra have been interpreted assuming C2v symmetry for the Zn(NH3)2I2 complex structure. The skeletal stretching metal-ligand modes vs(ZnN), vas(ZnN), vs(ZnI), vas(ZnI) as well as the three bending modes δ(NZnN), δ(IZnI) and δ(IZnN) were assigned by comparison with the spectra of Zn(NH3)2C12 and Zn(NH3)2Br2, and by the observed isotopic shifts of the frequencies. A normal coordinate analysis for the whole complex was carried out using the Local Symmetry Force Field Model.

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn - Teller Effect in Molecules.

Intrinsic and extrinsic forces behind the distortion in metal atom clusters can be readily distinguished provided that the clusters are embedded in a suitable ligand environment and that the tunneling of the protons in the peripheral ligands is then analyzed by inelastic neutron scattering. For the [Cr3 O(OOCCH3 )6 (H2 O)3 ]Cl⋅6 H2 O model system studied, the tunneling process is very sensitive to the local environment. Thus a tool is available to allow a better assessment of the cause of structural distortions.

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn – Teller Effect in Molecules

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn – Teller Effect in Molecules

Precision test of charge symmetry of nuclear force via photonuclear reactions of 4He

The (γ,p) and (γ,n) reactions of 4He at the energy of the giant dipole resonance provide a very sensitive tool for investigation of the charge symmetry in nuclear forces. In order to search for a possible breaking of the charge symmetry, we are going to make high-precision measurement of the reaction cross sections by using a Laser-Compton scattered γ-ray beam and a time projection chamber. Since both reaction cross sections are measured simultaneously, the charge symmetry can be tested with high accuracy. In this paper we will show the present status of our project.

In-vivo assessment of anterior cruciate ligament strain during walking

The purpose of this study was to investigate the variability and symmetry of ground reaction force (GRF) measurements during walking, using time and frequency domain analysis. Means and standard deviations of selected GRF time and frequency domain parameters for the left and right sides were calculated from 10 trials of each side. The results showed that a 10-trial mean GRF frequency content meets acceptable variability limits (<10%), and confirms the hypothesis of gait symmetry. The time domain variable results in the vertical and anterior-posterior directions agree with previous findings. In contrast, time domain parameters in the medial-lateral component are characterised by substantial asymmetries, probably due to the high variability found in this axis. Results indicated that overall pattern examination of the GRF curves using frequency analysis instead of isolated time domain parameters, is a more appropriate procedure for GRF comparisons.

Raman and infrared vibrational spectra, ab initio calculations and normal coordinate analyses for 1,2-dimethyltetrachlorodisilane and 1,2-dimethyltetrachlorodisilane-d 6

The Raman spectra of CH 3Cl 2SiSiCl 2CH 3 and CD 3Cl 2SiSiCl 2CD 3 between 3000 and 30 cm −1 have been recorded at various temperatures. The infrared spectra at ambient temperature were recorded from 3000 to 50 cm −1. Both isotopomers exist as a mixture of gauche and anti rotamers at room temperature. The energy difference E anti− E gauche was determined from the Raman spectra as being −0.9±0.2 kJ mol −1 for CH 3Cl 2SiSiCl 2CH 3 and −1.2±0.2 kJ mol −1 for CD 3Cl 2SiSiCl 2CD 3. Assisted by ab initio calculations, the vibrational spectra have been assigned using C 2h symmetry for the anti rotamers and C 2 symmetry for the gauche rotamers. Scaled and unscaled harmonic frequencies and harmonic symmetry force constants have been reported for both rotamers, and normal coordinate analyses have been carried out. Potential energy distributions have been reported.