Phase increment analysis of damped Duffing oscillators

A phase increment method is introduced to construct the response curves for the damped Duffing oscillator in primary, superharmonic, and subharmonic resonances. Non-linear parameters can be arbitrarily large. The algorithm is numerically stable. All resonance response curves are constructed in a unified manner. Closed loop curves are obtained in subharmonic resonances as opposed to open ended ones predicted by the perturbation method. Higher order resonances are constructed without difficulties. Loops are also observed in superharmonic resonances when non-linearity is not small.     

The Grid Application Toolkit: Toward Generic and Easy Application Programming Interfaces for the Grid

Core Grid technologies are rapidly maturing, but there remains a shortage of real Grid applications. One important reason is the lack of a simple and high-level application programming toolkit, bridging the gap between existing Grid middleware and application-level needs. The Grid Application Toolkit (GAT), as currently developed by the EC-funded project GridLab, provides this missing functionality. As seen from the application, the GAT provides a unified simple programming interface to the Grid infrastructure, tailored to the needs of Grid application programmers and users. A uniform programming interface will be needed for application developers to create a new generation of "Grid-aware" applications. The GAT implementation handles both the complexity and the variety of existing Grid middleware services via so-called adaptors. Complementing existing Grid middleware, GridLab also provides high-level services to implement the GAT functionality. We present the GridLab software architecture, consisting of the GAT, environment-specific adaptors, and GridLab services. We elaborate the concepts underlying the GAT and outline the corresponding application programming interface. We present the functionality of GridLab's high-level services and demonstrate how a dynamic Grid application can easily benefit from the GAT. All GridLab software is open source and can be downloaded from the project Web site.     

Beyond G-band: a 235 GHz InP MMIC amplifier

We present results on an InP monolithic millimeter-wave integrated circuit (MMIC) amplifier having 10-dB gain at 235GHz. We designed this circuit and fabricated the chip in Northrop Grumman Space Technology's (NGST) 0.07-/spl mu/m InP high electron mobility transistor (HEMT) process. Using a WR3 (220-325GHz) waveguide vector network analyzer system interfaced to waveguide wafer probes, we measured this chip on-wafer for S-parameters. To our knowledge, this is the first time a WR3 waveguide on-wafer measurement system has been used to measure gain in a MMIC amplifier above 230GHz.     

A backscattering model for ocean surface

A surface scattering model based on an approximate solution of the integral equations for the surface tangential fields has been developed for non-Gaussian distributed, finitely conducting surfaces. It consists of two parts. One part is proportional to the surface roughness spectrum, and the other to the surface bispectrum. The bispectrum part comes into the model when the third-order surface statistics are included. While the second-order statistics account for the wind directional dependence, the third-order statistics account for the dependence on the sense of direction of the wind. Thus, it is the critical part for explaining the difference between upwind and downwind observations. In general, the bispectrum is a complex quantity and the asymmetric effect of the sea surface is represented by its imaginary part. The model characteristics, such as polarization and azimuthal dependence, are illustrated through numerical calculations. The predictions of the model are compared with field measurements, and excellent agreement is obtained     

On the Performance of a Feedback Communication System Utilizing a Cumulative Decision Scheme

A cumulative decision scheme that can be employed in a feedback communication system is treated. Any decision to decode depends upon all messages that have been received prior to the decision. The average error over all transmissions as well as the forward error may be controlled. Performance is compared to an error-detection repeat-request noncumulative scheme utilizing group codes. Optimal performance of the cumulative scheme with respect to the noncumulative scheme is given for short-length best group codes. It is also demonstrated that the use of feedback does not necessarily increase appreciably the amount of hardware necessary to effect error control.     

Energizing Implantable Transmitters by Means of Coupled Inductance Coils

In the study of energizing implantable oscillators by coupling of inductance coils, it is pointed out that the best stability is not necessarily obtained where the magnetic flux density takes its maximum. The conversion of the induced ac voltage to a useful dc voltage can be made in conventional rectifier circuits, but great improvement in operation and economy is offered by transistor rectifier circuits. Two types of transistor rectifiers?the common-base and the common-collector arrangements?are discussed in detail.     

Hypersonic absorption of liquids determined from spontaneous and stimulated Brillouin scattering

The Brillouin linewidth at acoustic frequencies of several 10⁹Hz was measured for CS2CCl4acetone, and C6H6. Experimental data were compared with values calculated from the theory of sound propagation under the assumption of a single relaxation frequency. Good agreement was found for the pure liquids except for C6H6. Extending a theory of binary mixtures from ultrasonic to hypersonic frequencies, we were able to account for the experimentally determined Brillouin linewidths in the mixed system CS2-CCl4.     

A phase matrix for a dense discrete random medium: evaluation ofvolume scattering coefficient

In the derivation of the conventional scattering phase matrix of a discrete random medium, the far-field approximation is usually assumed. In this paper, the phase matrix of a dense discrete random medium is developed by relaxing the far-field approximation and accounting for the effect of volume fraction and randomness properties characterized by the variance and correlation function of scatterer positions within the medium. The final expression for the phase matrix differs from the conventional one in two major aspects: there is an amplitude and a phase correction. The concept used in the derivation is analogous to the antenna array theory. The phase matrix for a collection of scatterers is found to be the Stokes matrix of the single scatterer multiplied by a dense medium phase correction factor. The close spacing amplitude correction appears inside the Stokes matrix. When the scatterers are uncorrelated, the phase correction factor approaches unity. The phase matrix is used to calculate the volume scattering coefficients for a unit volume of spherical scatterers, and the results are compared with calculations from other theories, numerical simulations, and laboratory measurements. Results indicate that there should be a distinction between physically dense medium and electrically dense medium     

CMOS on dual SOI thickness for optimal performance

A novel strained SOI process with dual SOI thickness has been demonstrated for the first time. Two different SOI thicknesses (Tsi) are obtained on the same wafer for n- and p-channel devices using one additional photo masking step. Device data shows the S/D junction capacitance is reduced by 12% without any degradation in the driving current. A thicker SOI is used for p-channel devices to increase the SiGe recess depth and volume for the embedded S/D SiGe. The driving current is improved by 15% as a result of the larger compressive stress compared to a smaller SOI thickness. Dual SOI thickness is proved to be a viable strategy for independently optimizing n- and p-channel devices.     

Electrically compensated Fourier transform ion cyclotron resonance cell for complex mixture mass analysis

Complex natural organic mixtures such as petroleum require ultrahigh mass spectral resolution to separate and identify thousands of elemental compositions. Here, we incorporate a custom-built, voltage-compensated ICR cell for Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS), based on a prior design by Tolmachev to produce optimal mass resolution. The compensated ICR cell installed in a custom-built 9.4 T FTICR mass spectrometer consists of seven cylindrical segments with axial proportions designed to generate a dc trapping potential that approaches an ideal three-dimensional axial quadrupolar potential. However, the empirically optimized compensation voltages do not correspond to the most quadrupolar trapping field. The compensation electrodes minimize variation in the reduced cyclotron frequency by balancing imperfections in the magnetic and electric field. The optimized voltages applied to compensation electrodes preserve ion cloud coherence for longer transient duration by approximately a factor of 2, enabling separation and identification of isobaric species (compounds with the same nominal mass but different exact mass) common in petroleum, such as C(3) vs SH(4) (separated by 3.4 mDa) and SH(3)(13)C vs (12)C(4) (separated by 1.1 mDa). The improved performance of the ICR cell provides more symmetric peak shape and better mass measurement accuracy. A positive ion atmospheric pressure photoionization (APPI) petroleum spectrum yields more than 26,000 assigned peaks, Fourier-limited resolving power of 800,000 at m/z 500 (6.6 s transient duration), and 124 part per billion root mean square (rms) error. The tunability of the compensation electrodes is critical for optimal performance.