Offset Shift Research Articles

An Efficient Algorithm to the Simulation of Delay–Doppler Maps of Reflected Global Navigation Satellite System Signals

A new and efficient algorithm to compute delay-Doppler maps is presented. It improves by more than an order of magnitude the required computation time and memory resources. This approach is based on the derivation of explicit expressions of the space coordinates as a function of the delay offset and Doppler shift. Using this technique, the limitation posed by the number of sampling points of the observed surface is drastically attenuated, and a wide range of scenarios from low- to medium-height airborne-to-spaceborne scenarios can now be simulated with standard desktop computers.

Effect of slice angle on inhomogeneity artifact and its correction in slice‐selective MR imaging

AbstractThe inhomogeneity of a local magnetic field causes an image artifact of geometric distortion and intensity abnormality because of the slice offset and readout shift in slice‐selective MR imaging. It has been found that this artifact can be corrected by the projection of the slice offset onto the readout axis at a certain oblique slice angle. The slice angle for the artifact correction is determined by the amplitude of slice selection and readout gradients, and is independent of the magnetic field inhomogeneity and the main magnetic field direction. In addition, the existing view‐angle tilting technique is found to be valid only for the slice orientation orthogonal to the object axis. The slice angle effect on the inhomogeneity artifact was confirmed experimentally through phantom and volunteer's head imaging for both regular and view‐angle tilted spin echo sequences at 3 T. © 2009 Wiley Periodicals, Inc.Concepts Magn Reson Part A 34A: 238–248, 2009.

An improved in situ measurement of offset phase shift towards quantitative damping-measurement with AFM

An improved approach is introduced in damping measurement with atomic force microscope (AFM) for the in situ measurement of the offset phase shift needed for determining the intrinsic mechanical damping in nanoscale materials. The offset phase shift is defined and measured at a point of zero contact force according to the deflection part of the AFM force plot. It is shown that such defined offset phase shift is independent of the type of sample material, varied from hard to relatively soft materials in this study. This improved approach allows the self-calibrated and quantitative damping measurement with AFM. The ability of dynamic mechanical analysis for the measurement of damping in isolated one-dimensional nanostructures, e.g. individual multiwalled carbon nanotubes, was demonstrated.

Progression of osteoarthritis of the knee after unilateral total hip arthroplasty: minimum 10-year follow-up study

Patients undergoing total hip arthroplasty (THA) exhibit changes in the alignment of lower extremities following the procedure, and these changes may exert effects on other joints over the long-term. Therefore, we investigated the course of knee osteoarthritis in patients undergoing long-term follow up after THA, in addition to the relationship between the course of knee osteoarthritis and alignment of lower extremities. We retrospectively performed radiographic evaluation of the course of knee osteoarthritis (OA) after THA. Thirty patients undergoing successful unilateral THA were followed for a minimum of 10 years. Eleven (33%) subjects showed progression of medial tibiofemoral OA on the non-THA side, while only three (10%) showed progression on the THA side, and this difference was significant (P = 0.033). In addition, the mechanical axes on the THA side passed through more lateral regions of the tibial plateau than those on the non-THA side (P = 0.044). Medial tibiofemoral OA on the THA side was less likely to deteriorate than on the non-THA side. The reduced vulnerability to OA progression on the THA side may be due to the lower offset and resultant lateral shift in mechanical axes.

Accurate Assessment of Packaging Stress Effects on MEMS Sensors by Measurement and Sensor–Package Interaction Simulations

In this paper, packaging-induced stress effects are assessed for microelectromechanical systems (MEMS) sensors. A packaged MEMS sensor may experience output signal shift (offset) due to the thermomechanical stresses induced by the plastic packaging assembly processes and external loads applied during subsequent use in the field. Modeling and simulation to minimize the stress-induced offset shift are essential for high-precision accelerometers, gyroscopes, and many other MEMS devices. Improvement of plastic package modeling accuracy is accomplished by correlating finite-element analysis package models using measured material properties and package warpage. Using a refined reduced-order MEMS sensor and package interaction model, device offset is simulated, optimized, and compared with data collected from a unique three-axis accelerometer, which uses a single mass for all three axes sensing. As a result, this accelerometer has achieved very low offset in all axes over device operation temperature range of to . Device offset performance was improved by at least five times after the MEMS design optimization as compared with the one prior to the optimization.

Pathway of bichromatic high-order harmonic generation

We present a theoretical study of the pathway of harmonic generation in bichromatic linearly polarized laser fields. A 'harmonic-collapse' phenomenon is observed in the power spectrum for a particular value of the amplitude ratio of two components of the external field. We employ an offset frequency shift to the additional field to distinguish the harmonic pathway and then to explain the harmonic-collapse phenomenon. The harmonic intensity as a function of the relative amplitude ratio and, furthermore, the fine structure of the harmonic spectrum can be well understood on the basis of a pathway analysis.

Minimizing Spectral Leakage of Nonideal LINC Transmitters by Analysis of Component Impairments

LInear amplification with Nonlinear Components (LINC) is a distortion-free transmitter architecture under ideal conditions. However, in a realistic transmitter, imbalances such as dc offset, differential gain, and differential phase shift present in the quadrature modulators result in generation of out-of-band spectral components, even assuming that both amplifiers have identical characteristics. The level of distortion not only increases with the magnitude of the imbalances but also depends, to a large extent, on their relative phase arguments. The contribution of this paper is to provide a simplified characterization of the spectral leakage in the LINC transmitter in terms of quadrature modulator imbalances, with identical or mismatched amplifiers. This characterization allows identification of the transmitter with minimum spectral leakage under the constraint that the quadrature modulators perform equally well when used individually, i.e., in a transmitter composed of just the quadrature modulator followed by an amplifier. With reasonably small imbalances in the quadrature modulators and realistic amplifier mismatch, the spectral leakage at the output of a LINC transmitter driven by typical modulation schemes can be reduced by up to 10 dB, simply by a wise pairing of modulators

Heteronuclear isotropic mixing separated local field NMR spectroscopy

This paper presents a theoretical, numerical, and experimental study of a new class of separated local field (SLF) techniques. These techniques are based on the heteronuclear isotropic mixing leading to spin exchange via the local field (HIMSELF). It is shown that highly efficient and robust SLF experiments can be designed based on double channel windowless homonuclear decoupling sequences. Compared to rotating frame techniques based on Hartmann-Hahn cross polarization, the new approach is less susceptible to the frequency offset and chemical shift interaction and can be applied in the structural studies of macromolecules that are uniformly labeled with isotopes such as (13)C and (15)N. Furthermore, isotropic mixing sequences allow for transfer of any magnetization component of one nucleus to the corresponding component of its dipolar coupled partner. The performance of HIMSELF is studied by analysis of the average Hamiltonian and numerical simulation and is experimentally demonstrated on a single crystalline sample of a dipeptide and a liquid crystalline sample exhibiting motionally averaged dipolar couplings.

Cramer-Rao bounds of the frequency estimation in the time selective radio channels with Doppler spread

The mobile channel is slow fading and time selective, thus the multiplicative and additive noise of the channel will smear the spectral line, or arouse Doppler spread. This spread will make the parameters estimation accuracy degrade. The goal of this paper is to analytically assess this degradation when Carrier Frequency Offset (CFO) and Doppler shift exist jointly. Then the finite-sample Cramer-Rao Lower Bound (CRLB) is derived and close-form asymptotical expression is given for large-sample CRLB. These expressions give insights into the performance room for frequency estimation. Also the variance of Doppler shift estimator is simulated to illustrate the theoretical results.

Active and passive frequency stabilization for a Q-switched Z-fold radio-frequency-excited waveguide CO_2 laser with two channels

We report on passive offset frequency stability in free-running applications and active offset frequency stability achieved by use of a frequency-locking technique for a Q-switched Z-fold rf-excited waveguide CO2 laser with two channels. The laser structure of common electrodes and two channels has the advantage of compensating for the frequency variation caused by variations in temperature, cavity length, gas refractive index, and mechanical vibrations, so its offset frequency stability is higher than that of two separate lasers. In the experiments, the offset frequency shift was less than 6 MHz for 3 min in free-running mode. The technique of active offset frequency locking by counting was also introduced. The beat frequency shifting value was smaller than +/- 0.5 MHz in the long-term.

Near neighbor approximation in nuclear magnetic resonance.

A new way to deal with the excitation by multiple effective RF fields with interference is presented using the coherent averaging theory. It significantly simplifies the calculation of the effect of RF interference that occurs in the excitations by periodic pulses and phase-incremented pulses (PIPs). This approach shows that each neighboring RF field contributes to an excitation profile an offset shift, which is termed the Bloch-Siegert offset shift (BSOS). The BSOS depends not only on the strengths of both RF fields that interfere with each other but also on their relative phase between the two RF fields. Consequently, it can be positive, negative, and zero. In addition, the BSOS is also inversely proportional to the frequency separation of the two RF fields. Therefore, only a few near neighbors need to be taken into account in most cases, resulting in a near neighbor approximation (NNA). The BSOS for two multiband excitation profiles, one by a periodic pulse and the other by a PIP, are calculated using the NNA. The results are in good agreement with the computer simulated ones.

On the zero offset stability of thick film strain gauges

This paper presents results of work aimed at characterising the zero offset stability in novel thick film strain gauges. The devices studied arez‐axis (k33) load sensors fabricated on insulated stainless steel substrates and include examples of novel commercially developed force sensors. Devices loaded with compressive strains using a purpose designed test jig were found to exhibit a significant zero offset shift, which is negative up to a certain level (typically 1,000 micro strains) and then increasingly positive when strained beyond this point. Repeated cycles of loading then produced a certain level of stability until the previous maximum value of applied strain was exceeded. Temperature coefficient of resistance (TCR) measurements showed the devices to exhibit characteristics that depend significantly on the device geometry. The TCR was found to increase positively with increasing device thickness and surface area. The effect of overglazing the devices was found to decrease the TCR.

Nonlinear effects of radio-frequency interference in operational amplifiers

In this brief, the susceptibility of operational amplifiers to radio frequency interference (RFI) is studied by a new analytical model. The proposed model, in particular, points out the dependence of the RFI induced dc offset voltage shift in operational amplifiers on design parameters and parasitics, giving both a good insight into the nonlinear mechanisms involved in the phenomenon and a support to integrated circuit designers in order to develop high immunity operational amplifiers. The validity of the proposed approach is discussed comparing model predictions with the results of computer simulations and experimental measurements.

Correlation between nonionizing energy loss and the offset voltage shift in InP-InGaAs heterojunction bipolar transistors

Nonionizing energy loss (NIEL) calculations are reported for the neutron, electron, and gamma irradiation in InGaAs. We discuss the correlation between the calculated NIEL values and the experimentally observed offset voltage shift in InP-InGaAs heterojunction bipolar transistors.

Restoration of motion-related signal loss and line-shape deterioration of proton MR spectra using the residual water as intrinsic reference.

A postprocessing method to restore motion-related signal loss and line-shape deterioration in single-volume proton MR spectroscopy (MRS) is presented. Each acquisition is corrected by its phase offset and frequency shift, extracted from the residual water signal prior to averaging. Requirements are good gradient selection and selective suppression of CSF in residual water. Stimulated echo acquisition mode (STEAM) spectra (TE = 30 ms) were analyzed using the LCModel program to study gains in metabolite signal and spectral quality in five brain regions. Increases of total N-acetyl-aspartate concentrations of up to 5% were observed. The method may be beneficial for clinical examinations of less compliant subjects and for dynamic spectroscopy.

A high speed, precision voltage buffer in a submicron CMOS process

A new buffer architecture was introduced by Comer and Comer (1998, International Journal of Electronics, 84, 345). This buffer uses an active feedback network based on a transconductance amplifier. An implementation of the new buffer was done in a CMOS process. The buffer was intended for the output stage of a 10-bit video digital-to-analogue converter. The circuit was fabricated on the American Microsystems 0.6 μm process. Design specifications called for a gain accuracy of 0.1%, an offset voltage shift of no more than 1mV over a commonmode input range of 50% of supply voltage and a bandwidth of 500MHz. The actual circuit showed a gain error of less than 0.1%, a common-mode offset variation of less than 2mV, and a bandwidth of 450MHz.

Phase-dependent effects in bichromatic high-order harmonic generation

We address high-order harmonic generation with linearly polarized bichromatic fields, concentrating on a modulation in the harmonic yield as a function of the relative phase between the two field components, and on an offset phase shift of this modulation for neighboring cutoff harmonics. These effects have been recently observed in experiments where the relative phase between the two driving fields was controlled. Using the three-step model and the fully numerical solution of the time-dependent Schr\"odinger equation, we discuss the phase-dependent modulation and show that the offset phase is inherent to a particular set of semiclassical trajectories for the returning electron. These trajectories are identified using classical arguments and isolated by means of the saddle-point method, which allows a detailed investigation of their interference. Thus, by adding a second driving field whose amplitude lies within an adequate parameter range, one is able to single out a set of trajectories according to its behavior with respect to the relative phase. This effect is already present at the the single-atom-response level.

Thermal errors in media-separating housings of pressure sensors

Media-separating housings for pressure sensors are perspective constructions which enable pressure-sensitive elements to be protected from aggressive mediums. They also improve pressure sensor stability with regard to thermal shock. The systematic thermal errors which result from the placement of a pressure-sensitive chip in a media-separating housing are analyzed in this paper. The main systematic error which appears when using such constructions is a thermal offset shift caused by the presence of the separating steel diaphragm and the internally contained liquid when there is a change of temperature. In this paper, the calculated dependencies of such thermal offset shift are compared with the results of experimental investigations using various housing modifications.

Application of aluminum films as temperature sensors for the compensation of output thermal shift of silicon piezoresistive pressure sensors

Aluminum thin film resistors are proposed for use as temperature sensors for the compensation of the thermal sensitivity and offset shift of pressure sensor output. An experimental investigation of Al films with different thicknesses and heat treatment was carried out in order to optimize the electric parameters of such temperature resistors. It was found that films with a thickness 1.2 μm and thermal etched at 330°C for 72 h have good long-time stability, a specific resistance of 2.85 μΩ cm and a temperature coefficient of resistance of 4.33 × 10 −3/°C. The obtained results indicate that Al resistors can be used in an electrical circuit for the passive temperature compensation of the thermal shift of pressure sensor output within a temperature range of up to 125°C.

Surface Acoustic Wave Multiple Phase Shift Keying Modulator-Demodulator Circuits

Multiple phase shift keying technology is effectively used in various communication systems because of its high-capacity data transmission capability along a restricted passband. This-paper proposes a high-performance offset quadri-pulse shift keying modulator and demodulator with a new simple circuit configuration employing surface acoustic wave (SAW) devices. We propose two types of modulators (modulation and pulse pattern generation method) and a demodulator with a differential-operation SAW device. A fundamental experiment verified the feasibility of the circuits.