350,265 research outputs found
Pressure deformation of tires using differential stiffness for triangular solid-of-revolution elements
The derivation is presented of the differential stiffness for triangular solid of revolution elements. The derivation takes into account the element rigid body rotation only, the rotation being about the circumferential axis. Internal pressurization of a pneumatic tire is used to illustrate the application of this feature
Three-dimensional adaptive grid generation for body-fitted coordinate system
This report describes a numerical method for generating 3-D grids for general configurations. The basic method involves the solution of a set of quasi-linear elliptic partial differential equations via pointwise relaxation with a local relaxation factor. It allows specification of the grid spacing off the boundary surfaces and the grid orthogonality at the boundary surfaces. It includes adaptive mechanisms to improve smoothness, orthogonality, and flow resolution in the grid interior
States of Local Moment Induced by Nonmagnetic Impurities in Cuprate Superconductors
By using a model Hamiltonian with d-wave superconductivity and competing
antiferromagnetic (AF) orders, the local staggered magnetization distribution
due to nonmagnetic impurities in cuprate superconductors is investigated. From
this, the net magnetic moment induced by a single or double impurities can be
obtained. We show that the net moment induced by a single impurity corresponds
to a local spin with S_z=0, or 1/2 depending on the strength of the AF
interaction and the impurity scattering. When two impurities are placed at the
nearest neighboring sites, the net moment is always zero. For two unitary
impurities at the next nearest neighboring sites, and at sites separated by a
Cu-ion site, the induced net moment has S_z=0, or 1/2, or 1. The consequence of
these results on experiments will be discussed.Comment: 4 pages, 4 figure
Phase locked loop synchronization for direct detection optical PPM communication systems
Receiver timing synchronization of an optical pulse position modulation (PPM) communication system can be achieved using a phase locked loop (PLL) if the photodetector output is properly processed. The synchronization performance is shown to improve with increasing signal power and decreasing loop bandwidth. Bit error rate (BER) of the PLL synchronized PPM system is analyzed and compared to that for the perfectly synchronized system. It is shown that the increase in signal power needed to compensate for the imperfect synchronization is small (less than 0.1 dB) for loop bandwidths less than 0.1% of the slot frequency
Comparison of direct and heterodyne detection optical intersatellite communication links
The performance of direct and heterodyne detection optical intersatellite communication links are evaluated and compared. It is shown that the performance of optical links is very sensitive to the pointing and tracking errors at the transmitter and receiver. In the presence of random pointing and tracking errors, optimal antenna gains exist that will minimize the required transmitter power. In addition to limiting the antenna gains, random pointing and tracking errors also impose a power penalty in the link budget. This power penalty is between 1.6 to 3 dB for a direct detection QPPM link, and 3 to 5 dB for a heterodyne QFSK system. For the heterodyne systems, the carrier phase noise presents another major factor of performance degradation that must be considered. In contrast, the loss due to synchronization error is small. The link budgets for direct and heterodyne detection systems are evaluated. It is shown that, for systems with large pointing and tracking errors, the link budget is dominated by the spatial tracking error, and the direct detection system shows a superior performance because it is less sensitive to the spatial tracking error. On the other hand, for systems with small pointing and tracking jitters, the antenna gains are in general limited by the launch cost, and suboptimal antenna gains are often used in practice. In which case, the heterodyne system has a slightly higher power margin because of higher receiver sensitivity
- …