Asymmetric Angles Research Articles

Dosisverteilungen asymmetrischer Felder: Vergleich des Bestrahlungsplanungssystems Helax-TMS mit dem selbstentwickelten 2D-Berechnungsprogramm ASYMM

The purpose of this investigation was to compare the commercial 3D-treatment planning system Helax TMS to a simple 2D program ASYMM, concerning the calculation of dose distributions for asymmetric fields. The dose calculation algorithm in Helax-TMS is based on the polyenergetic pencil beam model of Ahnesjö. Our own developed 2D treatment planning program ASYMM, based on the Thomas and Thomas method for asymmetric open fields, has been extended to calculate the dose distributions for open and wedged fields. Using both methods, dose distributions for various asymmetric open and wedged fields of a 4-MV Linear accelerator were calculated and compared with measured data in water. The agreement of the Helax-TMS and the ASYMM with the experiment was good, whereas ASYMM showed a better accuracy for larger asymmetric angles. The explanation for this result is based on the consideration of beam hardening within the flattening filter and edges for different asymmetric settings in ASYMM algorithm. The TMS, however, owns the diverse possibilities that the 3D calculation and corresponding representation provide and holds better application opportunities in clinical routine.

Evaluation of lifting tasks frequently performed during fire brick manufacturing processes using NIOSH lifting equations

A fire brick manufacturing company with a high prevalence of low back injuries was selected for analysis of lifting tasks using the 1991 revised NIOSH lifting equations. We analyzed several manufacturing processes: forming, heating and packing processes involving frequent lifting and lowering in asymmetric postures. A questionnaire survey showed that weight of the load significantly influenced the incidence of back injuries and that workers who reported to have experienced back injuries were older than those who did not experience them. Composite Lifting Indices (CLI) based on the 1991 revised NIOSH lifting equations were calculated for 14 tasks of the forming process and five tasks of the heating/packing processes. Calculated CLIs for the tasks ranged from 0.86 to 8.8 (average 2.73) in the forming process and from 3.7 to 18.9 (average 11.12) in the heating/packing processes. The majority of the lifting tasks in this company exceeded the recommended weight limit (RWL). The results suggest that the tasks should be redesigned ergonomically to eliminate the risk factors that may cause low back injuries. Most of the jobs under study could be redesigned to lessen the biomechanical stress simply by making horizontal locations closer to a worker or by reducing the asymmetric angles. Relevance to industry During fire brick manufacturing processes, asymmetric lifting activities are frequently performed in Korea. It is crucial and beneficial to both management and labor to evaluate such tasks ergonomically based on the 1991 revised NOISH lifting equations for identifying risk factors that may cause musculoskeletal disorders.

Dips and backward peaks in the helium (e,2e) differential cross section at low energies

Two investigations have been carried out of the helium (e,2e) process. The first concerns the sharp dip that exists at an incident electron energy of 64.6eV and for equal energies and angles of the two outgoing electrons. The sensitivity of this dip to the asymmetry of the angles of the outgoing electrons has been measured and it has been found that the dip exists over a wide range of asymmetric angles, but with an almost constant angle between the two electrons. In the second investigation a new 'magnetic angle-changing' technique has been used to observe the two outgoing electrons when one of them moves in the same direction as the incident electron and the other moves in the opposite direction, and a peak has been found in the triple differential cross section when the incident electron energy is 40eV and outgoing energies are 4 and 11eV.

Multiple Machine Implementation of Enhanced Dynamic Wedge

Purpose: After acquiring 4 years of experience with Dynamic Wedge, a software-driven one-dimensional (1D) compensation system, we implemented a new software version called Enhanced Dynamic Wedge (EDW). The EDW allows larger (30 cm) and asymmetric field sizes and additional angles for wedged fields. We implemented this software on four similar dual-energy accelerators that also possess upper and lower physical wedge sets. Our goal was to implement EDW with one common wedge factor (WF) table and one set of treatment-planning files. Methods and Materials: We measured WFs with an ionization chamber and isodose profiles with both film and a diode array. We used a calculation scheme that requires only entry of the wedge angle and fixed jaw value. Filters for computerized treatment planning were configured for each wedge angle. We also examined to what degree the multileaf collimation (MLC) orientation, which is orthogonal to the EDW direction, was compromised for specific treatment sites. As a comparative test, we examined the dosimetric consistency for the 8 sets of physical wedges on the four machines. Finally, we updated our DW quality assurance program for EDW. Results: The measured EDW WF was common for all four machines to within ± 1.5% and the calculation scheme held to within 1.5%. The EDW isodoses were consistent among the machines as measured by film and diode array. The treatment-planning filters provided computed isodose profiles that were nearly identical to measured profiles. Regarding MLC orientation, we found that the collimator angle needed for EDW did not compromise isodose distributions, as apparent in measured isodoses and calculated dose–volume histograms. The consistency of the physical wedges did not fare as well. Two of the lower wedge sets had Wfs and profiles different (>3%) from the other wedge sets. Conclusions: We have successfully implemented EDW on four machines using only one WF table and one set of treatment-planning filters. The EDW provides for improved treatment techniques for particular sites due to the large field sizes and additional angles available. Daily treatment efficiency has increased because of the remote capability provided by EDW.

A novel power divider with arbitrary power division and high coupling efficiency with a single mode fibre

To improve the coupling efficiency of a conventional Ti: LiNbO3 channel waveguide with a single mode fibre, a promising Ti-Mg double diffused method has been employed to fabricate a single mode power divider. Calculated numerical results have revealed the feasibility of reducing coupling loss as well as radiation loss, and a set of efficient fabrication parameters for this single mode device can be established. The dependence of asymmetric branching angles and output dividing-power-ratios has been studied by adjusting the branching angle.

Effects of the roll angle on cruciform wing-body configurations at high incidences

Three cruciform wings were tested on a body at five roll angles and up to three longitudinal positions in a lowspeed wind tunnel, up to an angle of attack of a = 90 deg. The roll angle affects significantly the fin normal force coefficient. The normal force on the upper fins decreases to zero, at a > 40 deg, possibly because the vortex breakdown on the lower fins induces separated flow over the upper fins. As a consequence, a strong rolling moment is induced at these incidences at asymmetric roll angles. This rolling moment is independent of the wing axial position but proportional to the wing planform area, similarly to the fin normal force coefficient. This rolling moment is much larger than the rolling moment induced on symmetrical configurations by the asymmetric body vortices. The wing contribution to the side force is small compared with the body contribution at asymmetric roll angles. As a result, the maximum side force is not higher than that obtained at symmetric + and X attitudes.

Trunk Strength during Asymmetric Trunk Motion

It is important to understand how trunk strength varies as a function of workplace factors so that the work environment can be designed to minimize the risk of low back injury. In this study maximal trunk torque production around the lumbosacral junction was measured in 44 subjects as trunk concentric and eccentric isokinetic velocity and trunk asymmetric line of action were varied. Trunk torque decreased by approximately 8.5% of maximum for every 15 deg of asymmetric trunk angle. Increases in concentric velocity decreased trunk strength, whereas increases in eccentric trunk velocity increased strength. Significant interactions were also found, and it was determined that the common finding that eccentric strength exceeds concentric strength is true only for forward trunk angles at all asymmetric angles. These results should have significant implications for the design of manual materials handling tasks.

Propagation characteristics of optical guided waves in asymmetric branching waveguides

The propagation characteristics of optical guided waves in branching waveguides with asymmetric branching angles are investigated theoretically and experimentally. From the theory and the experiments performed on the titanium-diffused LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> branching waveguides, it has been made clear that, in such branching waveguides, optical power is divided asymmetrically, depending on the asymmetry of the branching angles. Therefore, branching waveguides with asymmetric branching angles can be used to tap a desired fraction of optical power from main waveguides.

A b i n i t i o investigation of geometry changes during inversion of NH3, NH2F, NHF2, NF3 and PH3, PH2F, PHF2, PF3

A b initio SCF molecular orbital calculations with complete geometry optimization have been performed using consistent basis sets for each member of the series NH3, NH2F, NHF2, NF3 and PH3, PH2F, PHF2, PF3. The calculations were repeated using the same basis sets with the molecules constrained to the planar configuration which is the transition state for inversion, all other geometrical parameters being energy optimized. In the planar configuration, shorter N–F, N–H, and P–H bonds resulted as well as a change from the nearly equal pyramidal bond angles to highly asymmetric planar bond angles with &amp;HXH≳ &amp;HXF≳ &amp;FXF. Omission of polarization functions from the basis set produced longer P–N and N–F bonds. Regardless of the inclusion or exclusion of d atomic orbitals in the basis set, substitution of fluorine for hydrogen yields regular increases in inversion barrier heights. Exclusion of d atomic orbitals results in inversion barriers that are smaller by nearly the same amount for all molecules in a series. The increase in barrier with substitution of fluorine for hydrogen is correlated with an increase of s character in the lone pair. Dipole moment and components, bond moments, and lone pair moments are discussed. Effects of varying the d orbital exponent coefficient on the central atom were examined.

Hypothesis on the role of liganded states of proteins in energy transducing systems

In energy transducing systems the direction of energy transfer is proposed to be maintained by the synchronized turnovers of the conformational change of one protein coupling up to affect another. Catalysis by those systems implies, therefore, that under new space restrictions the groups of the transducing enzyme increase and decrease reactivity between themselves, with activatory and/or inhibitory ligands (H +, H 2O, metals, etc.) and with the electron shells of the reactant molecules. The exergonic reaction-dependent turnover of the forms of the enzyme within the transition complexes would be maintained, therefore, under asymmetric phase angles of conformational-dependent reactivity that would effectively restrict the microscopic reversibility of transducing systems. Some well known reactions, such as hemoglobin's Bohr effect, can be used to illustrate that microscopic (molecular) interactions subject to thermodynamic equilibria laws may similarly participate as driving forces in energy transducing systems. This would allow the thermodynamic description of the role of proton translocation as that of a modificatory force of the structural parameters of proteins. Similarly, the relationship between the liganded states of hemoglobin and its change in conformation has been used to develop an illustrative model relating changes in oxido-reduction of electron carriers to induced-fit effects leading to a sequence of ATPase forms in transition complexes which become stabilized as high energy intermediates under the constraints imposed by the membrane of energy transducing organelles.

Wide-Angle Bremsstrahlung

We have extended our earlier measurements of the cross section for wide-angle electron bremsstrahlung. Besides the data for symmetric final electron and photon angles already published, we report results for asymmetric angles. The circulating electron beam of the Cornell 10-GeV synchrotron struck a carbon target and was monitored by observing the forward bremsstrahlung beam. Wide-angle photons were counted in coincidence with the corresponding scattered electrons. The recoil momentum of the unobserved nucleus was minimized. The experimental cross sections are compared with the predictions of the Bethe-Heitler formula corrected for elastic and inelastic nuclear form factors and for virtual nuclear Compton scattering. The agreement is excellent, confirming the predictions of quantum electrodynamics for timelike electron four-momenta up to 1.2 GeV. If one assumes a deviation in the experiment/theory ratio proportional to the square of the final electron-photon invariant mass, the 95% confidence upper limit on the corresponding distance parameter is ${{\ensuremath{\Lambda}}_{(2)}}^{\ensuremath{-}1}=5.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ cm. The upper limit for a fourth-power deviation is ${{\ensuremath{\Lambda}}_{(4)}}^{\ensuremath{-}1}=6.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ cm.