Drift Characteristics Research Articles

Derivative Preprocessing and Optimal Corrections for Baseline Drift in Multivariate Calibration

The characteristics of baseline drift are discussed from the perspective of error covariance. From this standpoint, the operation of derivative filters as preprocessing tools for multivariate calibration is explored. It is shown that convolution of derivative filter coefficients with the error covariance matrices for the data tend to reduce the contributions of correlated error, thereby reducing the presence of drift noise. This theory is corroborated by examination of experimental error covariance matrices before and after derivative preprocessing. It is proposed that maximum likelihood principal components analysis (MLPCA) is an optimal method for countering the deleterious effects of drift noise when the characteristics of that noise are known, since MLPCA uses error covariance information to perform a maximum likelihood projection of the data. In simulation and experimental studies, the performance of MLPCR and derivative-preprocessed PCR are compared to that of PCR with multivariate calibration data showing significant levels of drift. MLPCR is found to perform as well as or better than derivative PCR (with the best-suited derivative filter characteristics), provided that reasonable estimates of the drift noise characteristics are available. Recommendations are given for the use of MLPCR with poor estimates of the error covariance information.

Temperature Self-Compensated Lithium Tantalate Piezoelectric Gyroscope for Higher Stability

We are studying the flexura H-type vibrational gyroscope using a LiTaO3 single crystal with large electromechanical coupling coefficients. The H-type LiTaO3 piezoelectric gyroscope sharply suppresses leakage output. As a result, temperature characteristics of drift and sensitivity can be calculated using an equivalent circuit deduced from the experiment. The resonant frequency and Q-value of the X mode are stable with the temperature. However, the resonant frequency and the Q-value of the Z mode show complicated fluctuations with temperature due to the effects of the support and other factors. As a countermeasure, the possibilities of applying an automatic temperature characteristic compensation method with the monitor transducer in the drive mode of operating in nonresonant drive and resonant detection were studied. By adding a new monitor that detects the vibrational mode of the drive, we can establish a stable reference signal for the synchronous detection of output. It is possible to greatly improve the temperature characteristics of sensitivity and drift.

Temperature self-compensated lithium tantalate piezoelectric gyroscope for higher sensitivity and stability

A new H-type gyroscope using a single LiTaO 3 crystal that combines the H-type vibrational mode with a tuning fork type vibrational mode is proposed. This greatly suppresses leakage output from the piezoelectric gyroscope and also improves stability. The operation in the drive mode non-resonant condition and detection mode resonance condition is also proposed. It is possible to increase the sensor sensitivity remarkably because the drive voltage can be increased. In addition, an equivalent circuit constant including the leakage output could be accurately deduced. Automatic compensation of temperature characteristic for angular velocity detection sensitivity and drift is examined with the simple equivalent circuit. By adding a new sensor that detects the drive vibrational mode, we can produce a stable reference signal for the phase detection of output. This shows that it is possible to greatly improve the temperature characteristic of sensitivity and drift.

Electromigration-induced drift in damascene and plasma-etched Al(Cu). I. Kinetics of Cu depletion in polycrystalline interconnects

In this work, a direct and quantitative comparison is presented on the rate of electromigration-induced Cu depletion for polycrystalline damascene and reactive ion etched (RIE) Al(Cu). Kinetic data are derived from the incubation time, obtained from drift characteristics of both unpassivated and passivated Blech-type test structures between 155 and 230 °C. Since the incubation time represents the time necessary for the electron wind to deplete the critical length free of Cu, both electromigration (EM)-threshold and the rate of Cu depletion was systematically investigated. For the latter specific microstructural features, related to Al2Cu precipitate morphology and distribution, are discussed. EM-threshold on the other hand is a more intrinsic characteristic of the interconnect, depending on geometrical and mechanical properties (like aspect ratio and encapsulation). For geometrically equivalent, unpassivated structures, it was found that the improvement in incubation time for the damascene implementation is predominantly controlled by a higher critical length caused by its encapsulation inside the dielectric. For passivated structures, the impact of encapsulation on enlarging the maximum elastic stress buildup becomes similar. As a result, the difference in threshold between passivated damascene and RIE was observed to decrease. The incubation time in passivated structures becomes more importantly controlled by the kinetics of Cu depletion. It is demonstrated that it is most effective to maximize the degree of intergranular θ precipitation to retard the Cu depletion rate in polycrystalline structures. Implications on the relative EM performance under operating conditions for damascene and RIE Al(Cu) are also discussed.

A sequential method for control parameters in stabilized ALOHA systems

In previous studies, a criterion has been developed that guarantees stability of a slotted ALOHA system, provided the offered load is below a certain upper bound. This is done by selecting the control parameters through consideration of the estimated drift characteristics. A new joint drift analysis is presented that provides a sequential method for choosing control parameters so as to eliminate bistable operation and guarantee system stability not only below the upper bound referred to earlier, but also above the bound. In addition, the proposed strategy achieves maximum throughput for the system.

Singular plasma disturbances in the low‐latitude F region

We describe here a new phenomenon characterized by unusual patterns of ion drifts inside ion density depletion regions observed by the AE‐E satellite in the low‐latitude F region. In about 30 depletions, vertical ion drift relative to the background was upward on the western sides, downward on the eastern sides, and zero near the middle where the density depletion was greatest. These drift characteristics are distinct from those observed in plasma bubble depletions. The structures reported here were observed on circular orbits below 300 km altitude and had density depletions of up to 2 orders of magnitude or more below the ambient ion density. The upward and downward drift excursions were up to 200 m/s relative to the background. Almost all these structures were observed over oceans or near coasts and largely between ±10° and ±30° dip latitude. The structures were observed mostly as isolated, single depletion regions with the majority of them about 250 km wide in the east–west direction. They occurred during quiet magnetic conditions with near‐equal occurrence frequencies in the premidnight and postmidnight periods. The characteristic density and drift signatures indicate westward propagating disturbances in which the bottomside F layer is first lifted and then returned back to its original position, leaving the ionosphere undisturbed after the disturbance passes by. The estimated speed of these disturbances is of the order of 200 m/s. These unique solitary plasma disturbances, which we designate as singular plasma disturbances, are associated with a propagating source of E×B drift, not driven by neutral perturbations at the altitude of observation.

Storm time dependence of equatorial disturbance dynamo zonal electric fields

We use Jicamarca radar observations of F region vertical plasma drifts and auroral electrojet indices during 1968–1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields. These electric fields result from the dynamo action of storm time winds and/or thermospheric composition changes driven by enhanced energy deposition into the high‐latitude ionosphere during geomagnetically active conditions. The equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high‐latitude currents. On the average, this process can be described by two basic components with time delays of about 1–12 hours and 22–28 hours between the high‐latitude current enhancements and the equatorial velocity perturbations. Our data indicate strong coupling between dynamo processes with different timescales. The short‐term disturbance dynamo drives upward equatorial drifts (eastward electric fields) at night with largest amplitudes near sunrise and small downward drifts during the day. These perturbation drifts are in good agreement with results from the Blanc‐Richmond disturbance dynamo theory. The dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise‐noon sector. In this case, the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions. We also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts.

Investigation of walk-out phenomena in SiC mesa diodes with passivation

Abstract The drift or “walk-out” of the breakdown voltage in 6H-SiC mesa diodes passivated by a double layer of 1000 A SiO 2 and 3000 A Si 3 N 4 was investigated. The drift characteristics of diodes having wet and dry oxide passivation were compared to each other and to diodes subjected to additional hydrogen plasma etching of the SiC surface prior to dry oxidation. The influence of the UV illumination supplied by a HeCd laser of wavelength 325 nm on the walk-out characteristics and on the reverse current was investigated. No significant differences in the amount of drift and saturation level of breakdown voltage was found between the different passivations. However, the saturation level was reached about one order of magnitude faster in the wet oxide. A significant difference was found in the level and time dependence of the reverse current under UV illumination between the wet and dry oxide passivated diodes. The results are consistent with the existence of large concentrations of positive charge and acceptor-type deep interface traps. The walk-out is the result of the acceptor states being filled by hot electrons through the mechanism of avalanche injection.

Recent sedimentation beneath the Deep Western Boundary Current off northern New Zealand

The triangular shaped region defined by Chatham Rise in the south, the Louisville Seamount Chain in the east and the Pacific/Australian plate boundary in the west is one of the most active sedimentary regions of the world ocean. The SW Pacific Deep Western Boundary Current (DWBC), with a transport of 20 Sv, flows through the area producing regions of scour, nepheloid layers and typical depositional bedforms. Sediment is supplied to the region by turbidity currents directly via Hikurangi Channel and by the DWBC, which removes material from Bounty Fan south of Chatham Rise, as well as by fallout of volcanic ash and pelagic biogenic material. The CaCO 3 content of the sediments is very much controlled by terrigenous dilution, with Chatham Rise having ∼ 60%, but Hikurangi Plateau (near the Channel), sited well above the 4750 m-deep CCD, having only ∼ 20%. Although there is much evidence of scour around pinnacles and in scoured, possibly furrowed, mud deposits seen on 3.5 kHz profiles, dilute nepheloid layers, slow geostrophic and measured velocities, photographic and sediment grain-size evidence do not indicate fast flows. Mudwaves are of the irregular, vertically migrating type (rather than progressive antidunes), suggesting flows < ∼ 0.10 m s −1. In common with other Southern Ocean areas, flows may have been strongest during glacial times. Hikurangi Channel delivers its turbidity currents into the path of the DWBC, which sweeps them along to create a deep-sea fan with the characteristics of a contourite drift, here termed a fan-drift. This is mantled with migrating, climbing mudwaves, which are ascribed to deposition from episodic turbidity currents travelling at more than 0.1 m s −1. The fan-drift forms on the right-hand side of a boundary channel along the foot of the 1000 m-high Rapuhia Scarp. It is interpreted as a large right-bank levee formed by turbidity currents overspilling the Channel, which also owes its origin to scour by the DWBC. The turbidite deposits are dominantly mud and the evidence of scour/deposition patterns around a swath-mapped seamount indicate the depositing flows to be consistent with the DWBC flow direction, demonstrating entrainment of the turbidity currents by the deep geostrophic flow. Patterns of sedimentation around the Louisville Seamount Chain indicate action of a strong filament of the DWBC on the east side of the seamounts at least as far north as 37°S, and a relative intensification of the current on the west side of the seamounts north of 38°S.

Airborne off-target losses and deposition characteristics from a self-propelled, high speed and high clearance ground sprayer

In order to quantify the drift and deposition characteristics of a self-propelled, high-speed, and high-clearance sprayer, a series of 15 field trials was carried out applying a herbicide:dye mix along a test swath. Three different types of nozzle tips were used, an XR11002 (Extended Range XR Teejet®), and two "low-drift" tips, a DG11002 (Drift Guard Teejet®) and a TT11002 (Turbo Teejet®). On-swath and off-swath deposits were sampled using petri-dish collectors, while the airborne cloud was sampled 5 m downwind of the swath using Rotorod® samplers. In wind speeds of 10 to 31 km h−1, airborne droplet drift was reduced by a factor of two with both "low drift" designs. The differences in the behaviour of the two low-drift tips from the standard tips were attributed to reductions in the total volume emitted as drift-prone droplets by the low-drift tips, resulting from their inherent design characteristics. On-swath deposit uniformity was best with the DG11002 tips and worst with the TT11002 tips, with the XR11002 tips being intermediate. Off-swath-deposits increased with wind speed. Off-swath deposits between 5 and 10 m were proportional to the total airborne mass at 5 m. Key words: Pesticide, Spra-Coupe, droplet drift, flat-fan tips, deposition variability, droplet size, droplet volume

Basic Characteristics of Beam Position Drift and Field Stitching Error Caused by Electron Beam Column Charging

The beam drift caused by column charging and its influence on field stitching error were experimentally studied in an electron optical column with a contaminated inner surface. The raw drift characteristics indicate that secondary electrons with an energy lower than that of an electron accelerated by a voltage equal to the deflection voltage move from the substrate to the electrode surface and are the main cause of charging. Pattern writing was performed to examine field stitching error. For a continuously moving stage, the errors are roughly as large as the drift and their direction and magnitude change dramatically between neighboring rows of fields. The results on stitching error can be explained very well by considering the details of the writing procedure and the drift characteristics.

A new multiprobe method of roundness measurements

This paper presents a new multiprobe method for roundness measurements called the mixed method. In this method, displacements at two points on a cylindrical workpiece and an angle at one of the two points are simultaneously monitored by two probes. The differential output of the probes cancels the effect of the spindle error, and deconvolving the differential data yields the correct roundness error. The mixed method is compared to the traditional 3-point method with respect to the transfer function and resolution. Unlike the 3-point method, the mixed method can completely separate the roundness error and the spindle error, and can measure high-frequency components regardless of the probe distance. Resolution can also be improved throughout the entire frequency domain by increasing angular separation of the probes. An optical sensor specifically suited to the mixed method is designed and used to make roundness measurements. A fiber coupler and single-mode fibers are used in the sensor to divide a light beam from a laser diode into two beams, resulting in a compact sensor with good thermal drift characteristics. The displacement meter of the sensor is based on the imaging system principle and has a resolution of 0.1 μm. The angle meter is based on the principle of autocollimation and has a resolution of 0.5 in. A measurement system is constructed to realize measurements of roundness by using the optical sensor. Experimental results confirming the effectiveness of the mixed method for roundness measurements are also presented in this paper.

Automated E-field scanning system for dosimetric assessments

The interest in accurate dosimetric measurements inside phantoms that simulate biological bodies has burgeoned since several regulatory commissions began calling for or recommending the testing for compliance with safety standards of low power devices. This paper presents a newly developed, robot-based system that allows automated E-field scanning in tissue simulating solutions. The distinguishing characteristics of the system are its high sensitivity and its broad dynamic range (1 /spl mu/W/g to 100 mW/g) over the entire frequency range (10 MHz to over 3 GHz) used for mobile communications. The reproducibility of the dosimetric evaluations has been shown to be considerably better than /spl plusmn/5%. This has been accomplished by the use of an improved isotropic E-field probe connected to amplifiers with extremely low noise and drift characteristics in conjunction with digital processing of the data. Special emphasis has been placed on system reliability, user-friendliness and graphic visualization of data.

Levitation drift of a magnet supported by a high- Tc superconductor under vibration

Since the discovery of high- T c superconductors, many kinds of applications have been proposed. Among them, the high- T c superconducting bearing is considered to be one of the most possible applications. The bearing depends on the supporting force between a permanent magnet and a superconductor, caused by the flux pinning of high- T c superconductors. In this paper, the stability of levitation is discussed experimentally under external vibration. Then it shows the levitation drift for sintered YBaCuO, melt-quenched YBaCuO and melt-powder-melt-growth BiSrCaCuO. The characteristics of drift are explained as a relation with the force-displacement hysteresis. A dynamical model of the magnet and high- T c superconductor is also proposed to give the drift a physical meaning numerically.

A new generation of absolute gravimeters

We describe the design improvements incorporated in a new generation of absolute gravimeters, the FG5. A vertically oriented (in-line) interferometer design is used to remove the influence of floor vibration and tilt on the optical path length. The interferometer uses an iodine-stabilized laser as a primary length standard, with circuitry for automatic peak detection and locking. The seismic isolation system is an active long-period seismometer (Super Spring). The new design has improved passive isolation and thermal drift characteristics over previous systems. Programming flexibility and control of the test mass trajectory have been improved. The computer system has also improved real-time analysis and system capability. The FG5 instrument has a higher level of robustness, reliability and ease of use. These design advances have led to an instrumental uncertainty estimate of 1,1 × 10-8 m s-2 (1,0 μGal). Instrument agreement among nine similar devices is 1,8 μGal and observations under optimal conditions exhibit standard deviations of 5 μGal to 8 μGal.

On the spanwise correlation of vortex shedding from a circular cylinder at high subcritical Reynolds number

The three-dimensionality of the vortex shedding from a circular cylinder at high subcritical Reynolds number (4.3×104) has been studied, focusing on the characteristics of the vortex shedding phase drift and correlation along the cylinder span. Short time integration of the correlation coefficient, based on eight shedding cycles, showed that there were strong oscillations in the degree of correlation of the vortex shedding, and that these oscillations showed strong regularity having periods around 10–20 times the Strouhal period. These oscillations started when exceeding separations of Δz/d≊1 between the measurement points, and remained up to the largest case studied (Δz/d=6). The phase drift angle between two points at different spanwise positions was analyzed, showing that at the transition separation (Δz/d≊1) the probability distribution changed from being narrow banded to become more broad banded and closely Gaussian for an intermediate spacing of 2&amp;lt;Δz/d&amp;lt;4, and almost uniform for Δz/d=6. For all different separations studied (0.25&amp;lt;Δz/d&amp;lt;6), the probability distribution of the phase drift angle had a zero mean, indicating that the vortex shedding was, on the average, parallel to the cylinder.

Coordinated stable auroral red arc observations: Relationship to plasma convection

During the March 20‐22, 1990, magnetic storm, Millstone Hill radar and DMSP satellite observations detailed the conditions surrounding the occurrence of a SAR are which was observed continuously through an 8‐hour interval from dusk till past midnight in the North American sector. All‐sky imaging with a 630.0‐nm imager continually monitored the two‐dimensional position and magnitude of the SAR arc emission while radar scans and satellite overflights measured magnetospheric inputs and ionospheric response. The arc Was colocated with a deep, narrow plasma trough and a region of enhanced westward plasma convection of similar width situated immediately equatorward of the low‐latitude extent of plasma sheet particle precipitation. A region of low‐energy ion precipitation was observed at the equatorward edge of the SAR arc during a period of spatial/temporal coincident satellite/radar observations near the Millstone Hill longitude. The width of the SAR arc and related phenomena was of the order of 2°, and the ∼200‐R emission was associated with an electron temperature of ∼3500°K and a 10x reduction of plasma density at an altitude of 450 km. The best‐fit model for the emission intensities of both the SAR arc and the background airglow suggests that either the electron temperature at the center of the SAR arc was somewhat higher than observed by the radar (∼4000°K), or the neutral densities, [O2] and [O], were increased by factors of 2 and 4, respectively, with respect to the MSIS values. The ionospheric trough and a colocated region of enhanced sunward convection (500 ‐ 1700 m s−1) were observed in conjugate hemispheres throughout the local time range 18 ‐ 02 MLT. The convection feature seen in association with the SAR arc had many of the characteristics of a subauroral ion drifts (SAID) event; we report here the first long‐duration observations of a colocated SAID/SAR arc event. A narrow ionospheric trough developed during the interval when the SAID velocity was &gt;1000 m s−1 and was accompanied by a weak (100 R) 630.0‐nm emission. As the velocity fell to ∼700 m s−1, the density in the trough recovered somewhat, and the arc intensity rose to ∼300 R above background. This brighter period of the SAR arc occurred within a fossil trough/SAID. We conclude that there is a close spatial and temporal association among these three types of subauroral low‐altitude phenomena ‐ the SAR arc, the SAID event, and the fossil (convection‐related) trough ‐ and that this is indicative of the interrelationship of the magnetospheric processes and boundaries which are involved in their formation.

Dynamic characteristics of a resonating force transducer

Abstract Force transducers employing mechanical double-ended tuning-fork (DETF) resonators are very useful due to their virtual digital output, which allows easy interfacing with computers. The devices have excellent stability, inherent low hysteresis, low drift, high resolution and excellent static characteristics. When an applied force is undergoing dynamic changes, inertial and damping considerations apply. A technique for demodulation of the modulated signal from a DETF subjected to a dynamic applied force is described. A 50 N force transducer having an unloaded natural frequency of 4 kHz has been subjected to a periodically varying force of ±1 N superimposed on a 10 N static force by means of a mass connected to a mechanical vibrator. The frequency of the varying force has been taken up to 400 Hz and the DETF responds at this frequency.

On-Machine Measurement of Large Mirror Profile by Mixed Method

This paper presents a new differential method called the mixed method, which was developed to measure the profile accurately under the circumstances of on-machine measurement. In comparison with the 2-point method, this method can more remarkably reduce the datum errors due to scanning, vibration and thermal drift. This method also has the advantage of obtaining the high-frequency component of profiles accurately. An optical sensor was designed and constructed to realize both the 2-point method and the mixed method. With a modulation technique, the sensor has been made to have good thermal drift characteristics. It can measure the displacement and angle of two points on a mirror surface simultaneously with a resolution higher than 0.1μm and 1. Using this sensor ; an on-machine measurement system has been constructed, and measurements of the straightness of cylindrical mirrors have been attempted with the 2-point method and the mixed method. Comparing the results, the favorable characteristics of the mixed method have been confirmed.

Magnetopause plasma transients: signatures in the auroral ionosphere

The magnetopause and adjacent boundary layers of the Earth's magnetosphere play important roles in transferring momentum and energy from the solar wind to the magnetosphere-ionosphere system. The details of the different boundary processes, their ionospheric signatures and relative importance are not well known at present. Particle precipitation, field-aligned current, auroral emission, ionospheric ion drift and ground magnetic perturbations are among the low-altitude parameters that show signatures of various plasma processes in the LLBL and the magnetopause current layer. Magnetic merging events, Kelvin-Helmholtz waves, and pressure pulses excited by the variable solar wind/magnetosheath plasma are examples of boundary phenomena that may be coupled to the ionosphere via field-aligned currents. In this paper, attention is focussed on a specific category of auroral activity occurring in the cusp/cleft region predominantly during the southward directed interplanetary magnetic field (IMF). Co-ordinated observations from the ground and satellites in polar orbit have been used to study the temporal/spatial development of the events in relation to the background patterns of particle precipitation and ionospheric convection as well as the field-aligned current and ion drift characteristics of the individual events. The auroral phenomenon is characterized by a sequence of elongated forms moving laterally into the polar cap. Spatial scales of major events repeating every 5–10 min are ∼200 km (N-S) times 300–1000 km (E-W). Smaller scale auroral structures with more irregular occurrence rates are observed at times. The preliminary evidence suggests that the motion pattern is regulated by the IMF orientation, that is, the direction of longitudinal motion along the polar cap boundary is determined by the IMF B Y polarity. The examples reported here occurred within 1000–1400 MLT, near the zero point potential line separating the morning and post-noon convection cells. During nonzero IMF B Y the auroral structures are associated with channels of enhanced zonal ionospheric ion flow and Birkeland current sheets of opposite polarity, imbedded within the larger scale IMF B Y -related cusp-mantle current system. These characteristics are discussed in relation to model predictions of ionospheric signatures of magnetopause plasma transients, with particular emphasis placed on impulsive magnetic merging events.