499 research outputs found
Symmetry of Magnetically Ordered Quasicrystals
The notion of magnetic symmetry is reexamined in light of the recent
observation of long range magnetic order in icosahedral quasicrystals [Charrier
et al., Phys. Rev. Lett. 78, 4637 (1997)]. The relation between the symmetry of
a magnetically-ordered (periodic or quasiperiodic) crystal, given in terms of a
``spin space group,'' and its neutron diffraction diagram is established. In
doing so, an outline of a symmetry classification scheme for magnetically
ordered quasiperiodic crystals is provided. Predictions are given for the
expected diffraction patterns of magnetically ordered icosahedral crystals,
provided their symmetry is well described by icosahedral spin space groups.Comment: 5 pages. Accepted for publication in Phys. Rev. Letter
Tooth Contact Shift in Loaded Spiral Bevel Gears
An analytical method is presented to predict the shifts of the contact ellipses of spiral bevel gear teeth under load. The contact ellipse shift is the motion of the tooth contact position from the ideal pitch point to its location under load. The shifts are due to the elastic motions of the gear and pinion supporting shafts and bearings. The calculations include the elastic deflections of the gear shafts and the deflections of the four shaft bearings. The method assumes that the surface curvature of each tooth is constant near the unloaded pitch point. Results from these calculations will help designers reduce transmission weight without seriously reducing transmission performance
Nonlocal vortex motion in mesoscopic amorphous Nb0.7Ge0.3 structures
We study nonlocal vortex transport in mesoscopic amorphous Nb0.7Ge0.3
samples. A dc current I is passed through a wire connected via a perpendicular
channel, of a length L= 2-5 um, with a pair of voltage probes where a nonlocal
response Vnl ~ I is measured. The maximum of Rnl=Vnl/I for a given temperature
occurs at an L-independent magnetic field and is proportional to 1/L. The
results are interpreted in terms of the dissipative vortex motion along the
channel driven by a remote current, and can be understood in terms of a simple
model.Comment: 4 pages, 3 figure
Application of Face-Gear Drives in Helicopter Transmissions
The use of face gears in helicopter transmissions was explored. A light-weight, split torque transmission design utilizing face gears was described. Face-gear design and geometry were investigated. Topics included tooth generation, limiting inner and outer radii, tooth contact analysis, contact ratio, gear eccentricity, and structural stiffness. Design charts were developed to determine minimum and maximum face-gear inner and outer radii. Analytical study of transmission error showed face-gear drives were relatively insensitive to gear misalignment, but tooth contact was affected by misalignment. A method of localizing bearing contact to compensate for misalignment was explored. The proper choice of shaft support stiffness enabled good load sharing in the split torque transmission design. Face-gear experimental studies were also included and the feasibility of face gears in high-speed, high-load applications such as helicopter transmissions was demonstrated
Face-gear drives: Design, analysis, and testing for helicopter transmission applications
The use of face-gears in helicopter transmissions was explored. A light-weight, split-torque transmission design utilizing face-gears is described. Face-gear design and geometry were investigated. Topics included tooth generation, limiting inner and outer radii, tooth contact analysis, contact ratio, gear eccentricity, grinding, and structural stiffness. Design charts were developed to determine minimum and maximum face-gear inner and outer radii. An analytical study showed that the face-gear drive is relatively insensitive to gear misalignment with respect to transmission errors, but the tooth contact is affected by misalignment. A method of localizing the bearing contact to permit operation with misalignment was explored. Two new methods for grinding of the face-gear tooth surfaces were also investigated. The proper choice of shaft stiffness enabled good load sharing in the split-torque transmission design. Face-gear experimental studies were also conducted. These tests demonstrated the feasibility of face-gears in high-speed, high-load applications such as helicopter transmissions
Computerized Simulation of Meshing of Conventional Helical Involute Gears and Modification of Geometry
An approach is proposed for computerized simulation of meshing of aligned and misaligned involute helical gears. Algorithms for TCA (Tooth Contact Analysis) computer programs were developed. Influence of misalignment on the shift of the bearing contact and transmission errors has been investigated. Numerical examples that illustrate the developed theory are provided
Computerized Design and Generation of Gear Drives With a Localized Bearing Contact and a Low Level of Transmission Errors
A general approach developed for the computerized simulation of loaded gear drives is presented. In this paper the methodology used to localize the bearing contact, provide a parabolic function of transmission errors, and simulate meshing and contact of unloaded gear drives is developed. The approach developed is applied to spur and helical gears, spiral bevel gears, face-gear drives, and worm-gear drives with cylindrical worms
Effect of biologically active additives based on the homogenate of drone larvae on microcirculation and metabolism in Nordic skiers
Objective: to study the effect of biologically active additives (BAA) based on the homogenate of drone larvae on microcirculation and metabolism in Nordic skiers. Materials and methods: 58 male skiers at the age of 18-20 years ranging from 1 category to CMS were divided into two groups: the main group (30 athletes) and the comparison group (28 athletes). The skiers of the main group used the homogenate of drone larvae daily at a dose of 10 mg/kg of body weight during 21 days. Athletes from the comparison group received potato starch (placebo). The study of the microcirculation system was performed with a laser analyzer of the capillary blood flow «LAKK-M» before the BAA administration, at the 1st, 10th and 21st days of the study and 30 days after the end of the BAA administration. Results: A significant increase in perfusion was observed in the experimental group (121%,
Non-Equilibrium Edge Channel Spectroscopy in the Integer Quantum Hall Regime
Heat transport has large potentialities to unveil new physics in mesoscopic
systems. A striking illustration is the integer quantum Hall regime, where the
robustness of Hall currents limits information accessible from charge
transport. Consequently, the gapless edge excitations are incompletely
understood. The effective edge states theory describes them as prototypal
one-dimensional chiral fermions - a simple picture that explains a large body
of observations and calls for quantum information experiments with quantum
point contacts in the role of beam splitters. However, it is in ostensible
disagreement with the prevailing theoretical framework that predicts, in most
situations, additional gapless edge modes. Here, we present a setup which gives
access to the energy distribution, and consequently to the energy current, in
an edge channel brought out-of-equilibrium. This provides a stringent test of
whether the additional states capture part of the injected energy. Our results
show it is not the case and thereby demonstrate regarding energy transport, the
quantum optics analogy of quantum point contacts and beam splitters. Beyond the
quantum Hall regime, this novel spectroscopy technique opens a new window for
heat transport and out-of-equilibrium experiments.Comment: 13 pages including supplementary information, Nature Physics in prin
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