Drift Characteristics Research Articles

Features of the capacitance-voltage characteristics in a MOS structure due to the oxide charge

MOS structures based on p-and n-type silicon and subjected to the effect of voltages of both polarities with a magnitude as large as 70 V are studied. In all cases, an increase in the effective positive charge at the Si/SiO2 boundary was observed. In the case of structures with p-Si, a steplike increase in the high-frequency capacitance in the inversion region at some value of the threshold voltage was observed. The increase in the capacitance and the threshold voltage were governed by the value of the effective charge and the area of the gate of the structure. The observed effect is accounted for by lateral diffusion of free electrons accumulated in the semiconductor in the vicinity of the gate contact. After completion of the effect of the voltage on the structures, the capacitance-voltage characteristics were recovered to the state close to the initial state in the relaxation time characteristic of reverse drift of ions and emission of charge carriers by tunneling from “slow” traps in the vicinity of the Si/SiO2 interface.

Drift and Hysteresis Characteristics of Drug Sensors Based on Ruthenium Dioxide Membrane.

The drug sensing properties of procaine and berberine drug sensors based on ruthenium dioxide thin film were investigated. Ruthenium dioxide (RuO2) membrane prepared using a sputtering method was used as substrates for the drug sensors. The procaine and berberine drug sensors were prepared using a drug-saensitive membrane that measured the procaine and berberine concentration in a linear range from 1×10-2 M to 1×10-6 M and from 1×10-2 M to 1×10-7 M, respectively. The drift rates and hyteresis widths of these ruthenium dioxide based drug sensors were also investigated.

SEISMIC FRAGILITY ANALYSIS OF FRAME STRUCTURES

A seismic fragility analysis of structures is essential to prediction of the building behavior that is likely to occur during earthquakes. Normally, the probability of failure of a structure over a specified period of time is obtained through a convolution of the fragility curve with the seismic hazard curve for the structure site. The fragility models and damage states probabilities serve as a basis for improving the structural codes and performance-based design. Thus, there is a need for relatively simple procedures for evaluating fragility data for decision-making. In this study, the peak story drifts of a building structure during earthquakes are used as an indicator of structural demands. An analytical solution for evaluating the statistical characteristics of peak story drifts of frame structures during earthquakes is proposed. Based on it, an approximate approach to constructing the seismic fragility curves for various states of damage for frame structures is developed.

Exploiting manufacturing variations for compensating environment-induced clock drift in time synchronization

Time synchronization is an essential service in distributed computing and control systems. It is used to enable tasks such as synchronized data sampling and accurate time-of-flight estimation, which can be used to locate nodes. The deviation in nodes' knowledge of time and inter-node resynchronization rate are affected by three sources of time stamping errors: network wireless communication delays, platform hardware and software delays, and environment-dependent frequency drift characteristics of the clock source. The focus of this work is on the last source of error, the clock source, which becomes a bottleneck when either required time accuracy or available energy budget and bandwidth (and thus feasible resynchronization rate) are too stringent. Traditionally, this has required the use of expensive clock sources (such as temperature compensation using precise sensors and calibration models) that are not cost-effective in low-end wireless sensor nodes. Since the frequency of a crystal is a product of manufacturing and environmental parameters, we describe an approach that exploits the subtle manufacturing variation between a pair of inexpensive oscillators placed in close proximity to algorithmically compensate for the drift produced by the environment. The algorithm effectively uses the oscillators themselves as a sensor that can detect changes in frequency caused by a variety of environmental factors. We analyze the performance of our approach using behavioral models of crystal oscillators in our algorithm simulation. Then we apply the algorithm to an actual temperature dataset collected at the James Wildlife Reserve in Riverside County, California, and test the algorithms on a waveform generator based testbed. The result of our experiments show that the technique can effectively improve the frequency stability of an inexpensive uncompensated crystal 5 times with the potential for even higher gains in future implementations.

Spray Drift Mitigation with Spray Mix Adjuvants

Numerous drift reduction adjuvants and spray deposition aids are available to applicators of crop production and protection chemicals. Performance of many of the newly introduced drift control adjuvants has not been well documented for aerial application. Four new drift control adjuvants were selected for drift studies in aerial applications. Deposition, downwind drift, and droplet spectra characteristics in a cotton canopy were collected on water sensitive paper (WSP) and mylar cards for measurement and analysis. The deposition, droplet size, droplet coverage, and total drops were highly correlated to the drift distance and treatments or adjuvants. Deposition on the monofilament lines generally decreased as sampling height increased for each treatment. The results will aid aerial applicators in selecting drift reduction agents to meet the drift mitigation criterion for a given application.

Townsend coefficient, escape curve, and efficiency of runaway-electron beam formation in argon

The ionization and drift characteristics of electrons in argon are simulated by the method of multi-particle dynamics. It is shown that, in argon (as well as in other gases studied earlier), the Townsend regime of ionization sets in even in strong fields if the electrode distance is much larger than the reciprocal Townsend coefficient. The dependences of the basic ionization and drift characteristics on the reduced field intensity are obtained, and an escape curve is constructed separating the region of effective electron multiplication from the region where the electrons leave the discharge gap having no time to multiply. The formation efficiency of a runaway-electron beam is calculated. It is shown that the dependence of the electrode voltage generating a given fraction of runaway electrons on the product of the pressure by the electrode distance has a form that qualitatively agrees with the runaway curve. When the efficiency is not too high (≤20%), the runaway curves virtually coincide with isoefficiency curves.

Townsend coefficient, escape curve, and fraction of runaway electrons in copper vapor

Ionization and drift characteristics of electrons in copper vapor in the presence of an external electric field are analyzed. In contrast to normal gases, in copper vapor, the excitation energy of lower states is significantly lower than the ionization potential and the excitation cross section is several times greater than the ionization cross section at the incident-electron energy on the order of the ionization energy. This can affect the characteristics of electron bunching in gas. It is demonstrated that, as in previously studied gases, the notion of the Townsend coefficient remains meaningful even in the presence of strong fields at which the electric force exceeds the electron drag force acting in gas. The dependences of the main ionization and drift characteristics on the reduced field strength, the escape curve (which separates the region of effective electron multiplication and the region where electrons leave the discharge gap without multiplication), and the curves of equal efficiency for the formation of runaway electrons are obtained. It is demonstrated that a relatively high excitation cross section of copper levels leads to a sharper peak on the dependence of the Townsend coefficient on the field strength and a narrower region of the effective electron multiplication in comparison with previously studied gases.

An earthquake scenario for the microzonation of Sofia and the vulnerability of structures designed by use of the Eurocodes

The study of the site effects and the microzonation of a part of the metropolitan Sofia, based on the modelling of seismic ground motion along three cross-sections are performed. Realistic synthetic strong motion waveforms are computed for scenario earthquakes ( M=7) applying a hybrid modelling method, based on the modal summation technique and finite differences scheme. The synthesized ground motion time histories are source and site specific. The site amplification is determined in terms of response spectra ratio (RSR). A suite of time histories and quantities of earthquake engineering interest are provided. The results of this study constitute a “database” that describes the ground shaking of the urban area. A case study of experiment-based assessment of vulnerability of a cast-in-situ single storey, industrial, reinforced concrete frame, designed according to Eurocodes 2 and 8 is presented. The main characteristics of damage index and storey drift are discussed for the purposes of microzonation.

Analysis of equatorial plasma bubble zonal drift velocities in the Pacific sector by imaging techniques

Abstract. Using 1024 nights of data from 2002–2005 taken by the Cornell Narrow Field Imager (CNFI), we examine equatorial plasma bubble (EPB) zonal drift velocity characteristics. CNFI is located at the Maui Space Surveillance Site on the Haleakala Volcano (geographic: 20.71° N, 203.83° E; geomagnetic: 21.03° N, 271.84° E) on the island of Maui, Hawaii. The imager is set up to view in a magnetic field-aligned geometry in order to maximize its resolution. We calculate the zonal drift velocities using two methods: a correlation routine and an EPB west-wall intensity gradient tracking routine. These two methods yield sizeable differences in the evenings, suggesting strong pre-local midnight EPB development. An analysis of the drift velocities is also performed based on the three influencing factors of season, geomagnetic activity, and solar activity. In general, our data match published trends and drift characteristics from past studies. However, we find that the drift magnitudes are much lower than results from other imagers at similar latitude sectors but at different longitude sectors, suggesting that zonal drift velocities have a longitudinal dependence.

Ionization and drift characteristics of electrons in copper vapor in electric field

The ionization and drift characteristics (Townsend coefficient, drift velocity, mean energy) of electrons in copper vapor occurring in a homogeneous electric field have been numerically simulated. Copper is of interest by offering an example of element with the peak excitation cross section being significantly greater than the ionization cross section. A two-branch curve of electron loss is constructed, which separates the region of effective electron multiplication and the region of significant runaway (from which electrons leave the discharge gap without multiplication). Owing to the large excitation cross section of copper, the upper and lower branches of the electron leaving curve are closer to each other for this metal vapor than for usual gases.

Nonintrusive characterization of the azimuthal drift current in a coaxialE×Bdischarge plasma

A diagnostic is developed for the nonintrusive study of the azimuthal drift current in the coaxial ExB discharge of a Hall plasma accelerator. The technique of fast current interruption is used to generate a signal on several loop antenna that circle the outer wall of the discharge channel. The signal on the antenna is recorded, and used to determine the spatial distribution of the azimuthal drift at the moment of current interruption. The results of the experiment are compared to estimates derived via prior intrusive measurements, and the intrusive estimates are found to predict the spatial characteristics of the azimuthal drift, but underestimate its total magnitude. The self-induced magnetic field is then calculated and added to the applied magnetic field. The peak total magnetic field is seen to shift 2-5mm towards the anode due to self-induction, and suffer a reduction in magnitude of 10%-15%. The peak in the total magnetic field is then found to more closely coincide with the peak of the measured electric field than the peak of the vacuum magnetic field. It is concluded that the self-induced magnetic field could be important to anomalous electron mobility in the Hall-effect thruster, and simulation efforts should try to include its impact.

Lifetime Estimation of Moems Devices

Generally, microelectro mechanical systems (MOEMS) devices require encapsulation for protecting their fragile and tiny inner components in a hermetically sealed cavity. Cavity hermeticity can be critical to the device performance and plays a vital role with respect to reliability and long-term drift characteristics of the MOEMS products. The paper presents a theoretical approach for estimation of lifetime of MOEMS devices in terms of cavity’s hermeticity to gases and water. The results are summarized as working maps for MOEMS packaging engineers, in terms of device cavity (internal package volume), equivalent leak rates, and equivalent size of interconnected defects in the bonding zone.

Terahertz radiation from InAs induced by carrier diffusion and drift

Terahertz (THz) radiation from a (100) oriented InAs surfaces is dominated by the photo-Dember effect. The strength of the radiation is influenced by screening the radiation with doped carriers. When irradiated by femtosecond pulses, the wafer with the lowest doping concentration radiates THz power nearly two orders higher than the wafer with highest doping concentration. With identical optical excitation and same doping concentration, a $p$-type InAs generates stronger THz waves than an $n$-type InAs due to the weaker screening effect. The low doping $p$-type InAs ($1\ifmmode\times\else\texttimes\fi{}{10}^{16}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$) sample is the strongest THz wave emitter among all the unbiased semiconductors we have ever tested with a Ti:sapphire laser oscillator. The drift-diffusion equation (DDE) is used in the study of carrier drift and diffusion as well as subsequent THz radiation from InAs wafers. The calculation explains well the experimental observation of the relationship between a THz electric field and the doping properties of InAs. The physical pictures of the carrier drift and diffusion characteristics in InAs surfaces are also clearly provided in this report.

A high precision temperature control system for CMOS integrated wide range resistive gas sensors

In this work we present an integrated interface for wide range resistive gas sensors able to heat the sensor resistance through a constant power heater block at 0°C---350°C operating temperatures. The proposed temperature control system is formed by a sensor heater (which fixes the sensor temperature at about 200°C), a R/f (or R/T) converter, which converts the resistive value into a period (or frequency), and can be able to reveal about 6 decades variation (from 10 K? up to 10 G?), and a digital subsystem that control the whole systems loop. This interface allows high sensibility and precision and performs good stability in temperature and power supply drift and low power characteristics so it can be used also in portable applications. Test measurements, performed on the fabricated chip, have shown an excellent agreement between theoretical expectations and simulation results.

Cryogenic low energy electron point source microscope

The design and performance of a cryogenic low energy electron point source microscope are described. The microscope can be immersed in liquid helium, thus allowing for investigations at cryogenic temperatures. The cryogenic environment is associated with a low fluctuation in the field emission electron beam current and, combined with a compact and rigid mechanical design, low mechanical drift characteristics.

Gravitational Symmetry Breaking Leads to a Polar Liquid Crystal Phase of Microtubules In Vitro

Recent space-flight experiments performed by Tabony's team provided further evidence that a microgravity environment strongly affects the spatio-temporal organization of microtubule assemblies. Characteristic time and length scales were found that govern the organization of oriented bundles under Earth's gravitational field (GF). No such organization has been observed in a microgravity environment. This paper discusses physical mechanisms resulting in pattern formation under gravity and its disappearance in microgravity. The subtle interplay between chemical kinetics, diffusion, gravitational drift, thermal fluctuations, electrostatic interactions and liquid crystalline characteristics provides a plausible scenario.

Comparisons of Drift Reducing/Deposition Aid Tank Mixes for Fixed Wing Aerial Applications

Abstract A field study was conducted to determine the influence of adding spray drift control/deposition aid products to tank mix solutions for fixed wign aerial applications. Downwind horizontal drift, vertical drift, and droplet spectra characteristics in a canopy top were collected on water sensitive paper (WSP) for measurement and analysis. Spread factors for each spray mix sample were determined and were used as part of the analysis procedure with the canopy measurements. DropletScan™ was used to analyze the WSP. Percent area coverage for the horizontal and vertical drift profiles was used as a means to separate differences in treatments. DropletScan™ with adjusted spread factor coefficients was used to calculate Dv.1, Dv.5, and Dv.9 at the canopy top for each treatment. Differences in products at all horizontal and vertical collector positions were measured. When compared to water, results show that some of the products did not provide any benefits for drift reduction and, in fact, may have increased the drift potential. A few of the products exhibited the potential to reduce the amount of drift. Droplet sizes for Dv.1, Dv.5, and Dv.9 increased with the addition of the drift control/deposition aid products into the tank mix. The increases were variable across products and aircraft.

Glacial Sediment Causing Regional‐Scale Elevated Arsenic in Drinking Water

In the upper Midwest, USA, elevated arsenic concentrations in public drinking water systems are associated with the lateral extent of northwest provenance late Wisconsin-aged drift. Twelve percent of public water systems located within the footprint of this drift (212 of 1764) exceed 10 microg/L arsenic, which is the U.S. EPA's drinking water standard. Outside of the footprint, only 2.4% of public water systems (52 of 2182) exceed 10 microg/L arsenic. Both glacial drift aquifers and shallow bedrock aquifers overlain by northwest provenance late Wisconsin-aged sediment are affected by arsenic contamination. Evidence suggests that the distinct physical characteristics of northwest provenance late Wisconsin-aged drift--its fine-grained matrix and entrained organic carbon that fosters biological activity--cause the geochemical conditions necessary to mobilize arsenic via reductive mechanisms such as reductive desorption and reductive dissolution of metal oxides. This study highlights an important and often unrecognized phenomenon: high-arsenic sediment is not necessary to cause arsenic-impacted ground water--when "impacted" is now defined as >10 microg/L. This analysis also demonstrates the scientific and economic value of using existing large but imperfect statewide data sets to observe and characterize regional-scale environmental problems.

Determining the stress and convergence at Beypazari trona field by three-dimensional elastic–plastic finite element analysis: A case study

In this paper, deformation and failure characteristics of the main drift, T-2000, and a roadway, T-3000 excavated for Beypazari trona (natural soda) underground mine, which is located in Ankara, Turkey, were investigated by in situ measurements and numerical analysis. T-2000 was planed as a main drift with a length of 965 m, 14° inclined and excavated with an area of 18 m 2. The T-3000 roadway was driven in the trona ore body for the first stope. Load and convergence measurements were carried out at seven stations installed in main drift (T2000) and roadway (T3000). Measurement results indicate that the total convergences at all the stations were below 1% of the total gallery height and deformation rates were reduced significantly. Three-dimensional numerical modeling was performed to analyze the deformation and failure behavior of the drift for three different models using an elasto-plastic finite element method (FEM) approach considering Drucker–Prager failure criterion. The results of the numerical analyses were found to be comparable with in situ measurements.

Drift Characteristics of a Moored Conductivity–Temperature–Depth Sensor and Correction of Salinity Data

Abstract The temperature and conductivity drift (time change of the characteristics) of moored SBE37IM conductivity and temperature (CT) sensors was investigated by pre- and postdeployment calibration of the Triangle TransOcean Buoy Network (TRITON). This buoy network comprises the western portion of the basinwide (Tropical Atmosphere Ocean) TAO/TRITON buoy array, which monitors phenomena such as El Niño and contributes to forecasting climate change. Over the time of deployment the drift of the temperature sensors was very small, within 3 mK of the postdeployment calibration data. The drift of the conductivity sensors was more significant. After 1 yr of mooring, conductivity drift observed in the shallowest layer (1.5–100 m) was positive and 0.010 S m−1 [equivalent to 0.065 (PSS-78) at 30°C and 6 S m−1; here, 1 S is 1 Ω−1] at 6 S m −1 on average. Drift observed in the thermocline layer (125–200 m) was also positive and 0.0053 S m−1 [0.034 (PSS-78)] at 6 S m−1 on average. Conversely, the drift of conductivity in the deepest layer (250–750 m) was 0.00002 S m−1 with a standard deviation of 0.001 S m−1 [0.0065 (PSS-78)]. Assuming a linear trend of conductivity drift with time, the authors attempted to correct the conductivity data using the postdeployment calibration data. The corrected data for about 80% of the sensors exhibited smaller differences than the uncorrected data when compared with the in situ conductivity–temperature–depth (CTD) data. However, the corrected salinity data became worse than the uncorrected data for about 20% of the sensors. The reasons for these errors are also discussed in this paper.