A stochastic model of the electrically stimulated auditory nerve:pulse-train response

The single-pulse model of the companion paper [1] is extended to describe responses to pulse trains by introducing a phenomenological refractory mechanism. Comparisons with physiological data from cat auditory nerve fibers are made for pulse rates between 100 and 800 pulses/s. First, it is shown that both the shape and slope of mean discharge rate curves are better predicted by the stochastic model than by the deterministic model. Second, while interpulse effects such as refractory effects do indeed increase the dynamic range at higher pulse rates, both the physiological data and the model indicate that much of the dynamic range for pulse-train stimuli is due to stochastic activity. Third, it is shown that the stochastic model is able to predict the general magnitude and behavior of variance in discharge rate as a function of pulse rate, while the deterministic model predicts no variance at all.     

Bidirectional Nerve Refractory Characteristics in Simulations of Direct and Remote Stimulation

The effects of remote stimulation on the refractory characteristics of myelinated nerve fibers were investigated using computer simulations of nerve action potentials, in response to spatially separated conditioning and test stimuli. The behavior of the test action potential was strongly influenced by its direction of propagation relative to that of the conditioning action potential. Under certain conditions, the variation of relative refractory period with conduction velocity (CV) changed from inverse, for propagation in opposing directions, to direct, for propagation in the same direction. A similar directionally dependent result occurred in the study of relative refractory period as a function of stimulus intensity. At certain interstimulus intervals, the test stimulus elicited action potentials which would conduct in the direction opposite to the conditioning action potential, but would not conduct in the wake of that conditioning action potential. These results are explained in terms of the spatial spread of stimulus current resulting from distant placement of the stimulating electrode in a volume conductor. Clinical repercussions of these results for correction of refractory period in collision neurography are discussed.     

Acoustically scanned low-coherence interrogated simultaneousmeasurement of absolute strain and temperature using highly birefringentfibers

We have utilized a traveling acoustic pulse in a two-mode optical fiber to create a moving beam splitter coupling light from LP₀₁ to LP₁₁ mode. As these optical modes have different group velocities, a variable intermodal delay is generated as a function of acoustic pulse position in the fiber. The device can be used as a receiving interferometer in low-coherence interferometry to scan time delay for carrying out fast extended range absolute measurement using simple analog electronic circuits. With this scanning technique we demonstrate measurement of absolute strain over 1600 με in the temperature range from 20 to 60°C with resolutions of the order of 40 με and 0.7°C, respectively, employing highly birefringent fibers as sensing elements     

Tightness estimation of fiber ribbons in a slot-type single-modeoptical-fiber cable

Tightness of fiber ribbons in a slot-type cable is estimated by measuring the temperature dependence of fiber strain due to temperature change for free fiber ribbons and those assembled in a cable. Fiber-strain measurements were carried out by an optical heterodyne detection technique for free nylon-jacketed and liquid-crystal-polymer (LCP)-jacketed fiber-ribbons, and for the cabled fiber ribbons. By comparing the thermal behavior of fiber strain for both states of jacketed fibers, it is found that the fiber ribbons are tightly accommodated in the slot-type cable in temperature regions over -15°C for nylon-jacketed fiber ribbons and 0°C for LCP-jacketed fiber ribbons under additional fiber-strain value of 0.015% through the cabling process. The fiber ribbons, which are tightly accommodated with suitable tension level through the process at room temperature, show reasonable thermal-strain behavior in comparison with the initially introduced fiber strain during the cabling process     

Estimation for a life model of transformer insulation undercombined electrical and thermal stress

A life model for power transformer insulation is proposed. It is the Arrhenius model with a weighting factor for the enhanced reaction under combined thermal/electrical stress. Laboratory tests are used to evaluate the model's parameters. The thermal and thermal/electrical stress aging data on Fish paper are presented and analyzed. The estimates from the life model are close to the experimental results. It is hoped that the life model is extendable to other engineering materials. The model's parameters can be evaluated from two laboratory tests, thermal aging and combined thermal/electrical aging. For the Fish paper, when thermal stress is increased by 30°C, the life is reduced by a factor of 2; at 70°C life was 238 hours and at 100°C life was 120 hours. The material life was further reduced by a factor of nearly 2 when subjected to thermal/electrical stress: at 80°C life was 200 hours, whereas at 80°C and 600 Vac life was 118 hours. Electrical stress is important in accelerating the material degeneration     

Correlation of the absence of the 630-nm band with the intensity ofphotobleaching of ionizing radiation-induced loss in undoped silicafibers at -55°C

A correlation is reported between the intensity of the 630-nm drawing-induced band in undoped silica-core fibers and the abatement of photobleaching by 865-nm light of ionizing radiation-induced loss at 865 nm following gamma-ray exposure at -55°C. At -55°C, undoped silica-core fibers, both low- and high-OH containing, and polymer and glass clad, show intense, 865-nm photostimulated recovery of ionizing radiation-induced loss near 865 nm when the 630-nm drawing-induced band is weak or not present. This photobleaching behavior contributed significantly toward the low induced loss demonstrated by these fibers during exposure, and their faster recovery after exposure at low temperature     

Moist-air attenuation at 96 GHz over a 21-km line-of-sight path

A propagation experiment at 96 GHz over a line-of-sight (LOS) path provided data on attenuation characteristics of atmospheric water vapor. Two consecutive time periods (three days in May and 1.5 days in August 1986) with a total of about 100 h of data on signal level and meteorological conditions were analyzed with respect to absolute humidity (3-21 g/m³) and temperature (4-32°C) variations. Experimental details, the data analysis, and a comparison with model predictions are discussed. The validity of the millimeter-wave propagation model is considered and it is concluded that the field experiment tends to uphold the validity of this model at 96 GHz     

Thermal effects of Brillouin gain spectra in single-mode fibers

Brillouin gain spectra in two 250-m-long single-mode fibers with GeO₂-doped core/pure-silica cladding (fiber A) and pure-silica core/F-doped cladding (fiber B) were measured at temperatures ranging from -40 to +60°C at a wavelength of 1.32 μm. The temperature coefficients of Brillouin frequency shift were found to be 1.17 and 1.33 MHz/°C for fibers A and B, respectively. Temperature coefficients of Brillouin gain bandwidth were found to be -0.12 and -0.10 MHz/°C. These measurements provide useful information for applications of stimulated Brillouin scattering     

Temperature dependence of the gain in erbium-doped fibers

The temperature dependence of the gain in erbium-doped fibers between -20 and +85°C is discussed. The characteristics of three types of erbium-doped fibers with different erbium concentrations and glass compositions are investigated. The gain decreased with increasing temperature at the rate of -0.07 dB/°C when pumped at 1.48 μm. The change in the gain was small when pumped at 0.98 μm. By measuring the change in the absorption and fluorescence spectra with temperature, it is deduced that the change in the gain is mainly due to the change in the saturated population inversion     

Rate dependent constitutive relations based on Anand model for92.5Pb5Sn2.5Ag solder

A rate dependent constitutive model, the Anand model, was applied to represent the inelastic deformation behavior for a Pb-rich solder 92.5Pb5Sn2.5Ag used in electronic packaging and surface mount technology. This rate dependent model is a unified viscoplastic constitutive model using an internal state variable, the deformation resistance, to describe the averaged isotropic resistance to macroscopic plastic flow. In order to obtain the acquired data for the fitting of the material parameters of this unified model for 92.5Pb5Sn2.5Ag solder, a series of experiments of constant strain rate test and constant load creep test were conducted under isothermal conditions at different temperatures ranged from -65°C to 250°C. A procedure for the determination of material parameters was proposed in this paper. Model simulations and verifications revealed that there are good agreements between model predictions and experimental data. Moreover, some discussions on using this rate dependent model in the finite element simulation of stress/strain responses of solder joints under thermal fatigue loading were presented     

Characteristics of planar n-p junction diodes made bydouble-implantations into 4H-SiC

Double implantation technology consisting of deep-range acceptor followed by shallow-range donor implantation was used to fabricate planar n⁺-p junction diodes in 4H-SiC. Either Al or B was used as the acceptor species and N as the donor species with all implants performed at 700°C and annealed at 1650°C with an AlN encapsulant. The diodes were characterized for their current-voltage (I-V) and capacitance-voltage (C-V) behavior over the temperature range 25°C-400°C, and reverse recovery transient behavior over the temperature range 25°C-200°C. At room temperature, the B-implanted diodes exhibited a reverse leakage current of 5×10^-8 A/cm² at a reverse bias of -20 V and a carrier lifetime of 7.4 ns     

Absolute radiometric calibration of the CCRS SAR

Determining the radar scattering coefficients from SAR (synthetic aperture radar) image data requires absolute radiometric calibration of the SAR system. The authors describe an internal calibration methodology for the airborne Canada Centre for Remote Sensing (CCRS) SAR system, based on radar theory, a detailed model of the radar system, and measurements of system parameters. The methodology is verified by analyzing external calibration data acquired over a six-month period in 1988 by the C-band radar using HH polarization. The results indicate that the overall error is ±0.8 dB (1σ) for incidence angles ±20° from antenna boresight. The dominant error contributions are due to the antenna radome and uncertainties in the elevation angle relative to the antenna boresight     

Read-disturb and endurance of SSI-flash E2PROM devicesat high operating temperatures

The high-temperature (T) reliability behavior of merged-transistor source side injection (SSI) flash nonvolatile memory (NVM) devices is evaluated in terms of endurance and disturb effects related to stress induced leakage current (SILC) and correlated with the high-T behavior (generation, anneal) of oxide traps. As compared to room-T, program/erase (P/E) cycling at 150°C results in an improved endurance due to an enhanced charge emission. The impact of the operating temperature on SILC-related disturb effects, on the other hand, depends on two combined effects in memory cells where large local charge trap-up influences the threshold voltage, V_t: 1) the T-enhanced trap generation and 2) the T-enhanced emission of trapped charge which influences the disturb field. In the case of the HIMOS-cell-which is discussed here-long-term nonvolatility can still be guaranteed at 150°C. Finally, bake tests at higher temperatures (250-300°C) have been performed in order to evaluate the persistence of the generated damage. It is found that bulk oxide traps are not cured by the bake and, therefore, no long-term relief of SILC-related disturb effects is expected at 150°C     

Stochastic Population Model for Electrical Stimulation of the Auditory Nerve

We have developed a biophysical model of a population of electrically stimulated auditory nerve fibers. It can be used to interpret results from physiological and behavioral experiments with cochlear implants and propose novel stimulation strategies. Our model consists of myelinated internodes described by a passive resistor-capacitor network, membrane capacitance, and leakage current at the nodes of Ranvier, as well as stochastic representations of nodal voltage-dependent channels. To approximate physiological properties measured in the auditory nerve (AN) of an acutely deafened cat, electrical parameters of the model fiber were chosen based on literature-reported values. Using our model, we have replicated the following properties within 10% of the reported feline single-fiber measurements: relative spread (5.8%), spike latency (630 mus), jitter (93 mus), chronaxie (238 mus), relative refractory period (4.6 ms), and conduction velocity (14 m/s). Moreover, we have successfully matched response characteristics of a population of fibers with the same number of diameter-distributed model fibers, enabling us to simulate responses of the entire AN. To demonstrate the performance of our model, we compare responses of a population of ANs stimulated with two speech encoding strategies, continuous interleaved sampling and compressed analog.     

A model for rapid thermal processing: achieving uniformity throughlamp control

A first-principles approach to the modeling of a rapid thermal processing (RTP) system to obtain temperature uniformity is described. RTP systems are single wafer and typically have a bank of heating lamps which can be individually controlled. Temperature uniformity across a wafer is difficult to obtain in RTP systems. A temperature gradient exists outward from the center of the wafer due to cooling for a uniform heat flux density on the surface of the wafer from the lamps. Experiments have shown that the nonuniform temperature of a wafer in an RTP system can be counteracted by adjusting the relative power of the individual lamps, which alters the heat flux density at the wafer. The model is composed of two components. The first predicts a wafer's temperature profile given the individual lamp powers. The second determines the relative lamp power necessary to achieve uniform temperature everywhere but at the outermost edge of the wafer (cooling at the edge is always present). The model has been verified experimentally by rapid thermal chemical vapor deposition of polycrystalline silicon with a prototype LEISK RTP system. The wafer temperature profile is inferred from the poly-Si thickness. Results showed a temperature uniformity of ±1%, an average absolute temperature variation of 5.5°C, and a worst-case absolute temperature variation of 6.5°C for several wafers processed at different temperatures     

Uniform durable thin dielectrics prepared by rapid thermalprocessing in an N2O ambient

Thin dielectrics grown on silicon wafers by rapid thermal processing in an N₂O ambient at temperatures of 1100°C, 1150°C, and 1200°C are discussed. The resulting films, in conjunction with an O₂ ambient control were characterized by thickness measurements and electrical performance. Dielectrics formed in N₂O in this temperature range were all superior to that prepared in an O₂ ambient in terms of interface state generation and flatband voltage shift after constant current stressing. Although all N₂O prepared samples exhibited similar cross wafer electrical uniformity, higher growth temperatures favored thickness uniformity. The electrical behavior of the N₂O wafers was not strongly dependent on growth temperature; however, a 60-s 1100°C post-oxynitridation N₂ anneal was found to significantly reduce subsequent electrical performance. It is also demonstrated that under optimum process conditions, high-quality uniform dielectrics can be formed by RTP in N₂O     

Time dependent breakdown of ultrathin gate oxide

Time dependent dielectric breakdown (TDDB) of ultrathin gate oxide (<40 Å) was measured for a wide range of oxide fields (3.4<|E_ox|<10.3 MV/cm) at various temperatures (100⩽T⩽342°C). It was found that TDDB of ultrathin oxide follows the E model. It was also found that TDDB t₅₀ starts deviating from the 1/E model for fields below 7.2 MV/cm. Below 4.8 MV/cm, TDDB t₅₀ of intrinsic oxide increased above the value predicted by the E model obtained for fields >4.8 MV/cm. The TDDB activation energy for this type of gate oxide was found to have linear dependence on oxide field. In addition, we found that γ (the field acceleration parameter) decreases with increasing temperature. Furthermore, it was found that testing at high temperatures (up to 342°C) and low electric field values did not introduce new gate oxide failure mechanism. It is also shown that TDDB data obtained at very high temperature (342°C) and low fields can be used to generate TDDB model at lower temperatures and low fields. Our results (an enthalpy of activation of 1.98 eV and dipole moment of 12.3 eÅ) are in complete agreement with previous results by McPherson and Mogul. Additionally, it was found that TDDB is exponentially dependent on the gate voltage     

Lifetime of thin oxide and oxide-nitride-oxide dielectrics withintrench capacitors for DRAMs

An investigation of the field acceleration of the time-dependent dielectric breakdown behavior of a thermal oxide and an oxide-nitride-oxide (ONO) dielectric on planar- and trench-cell MIS capacitors under a constant field stress of 5-9 MV/cm at 150°C is discussed. Defect-related and intrinsic failures are distinguished by a statistical analysis of the breakdown distributions. Planar- and trench-cell capacitors with an ONO dielectric exhibit reduced early failures and a more favorable field-acceleration behavior than capacitors with a thermal-oxide layer. A method which determines the number of intrinsic failures by extrapolation of the accelerated constant field stress data to the device area and down to the operational electric field strength is proposed. The extrapolation predicts, for trench-capacitor arrays with a 5-mm² active device area and a 13.5-nm oxide dielectric operating at 3 MV/cm and 150°C, a mean intrinsic failure rate slightly below 100 Fit in the first year, whereas trench structures with an ONO-dielectric reach the same number of cumulative failures after 1 million years     

Temperature rise for the human head for cellular telephones and forpeak SARs prescribed in safety guidelines

The bioheat equation is solved for an anatomically based model of the human head with a resolution of 3 × 3 × 3 mm to study the thermal implications of exposure to electromagnetic (EM) fields typical of cellular telephones both at 835 and 1900 MHz. It is shown that similar to the measured data, up to 4.5°C temperature elevation may be caused for locations of the pinna by a cellular telephone warmed by electronic circuitry to temperatures as high as 39°C with temperature increases for the internal tissues such as the brain and eye that are no more than 0.1°C-0.2°C higher than the basal values. Similar to previous studies by other authors, additional temperature increases due to EM fields of cellular telephones are fairly small and typically less than 0.1°C. Another objective was to study the thermal implications of the SAR limits for the occupational exposures of 8 W/kg for any 1 g, or 10 W/kg for any 10 g of tissue suggested in the commonly used safety guidelines. Such specific absorption rates (SARs) would lead to temperature elevations for the electromagnetically exposed parts of the brain up to 0.5°C with 10 W/kg for any 10 g of tissue resulting in somewhat higher temperatures and for larger volumes. Similar temperature increases are also calculated by increasing the arterial blood temperature, except that the temperature increases due to the SAR are for the more limited volume rather than the entire brain     

DC modeling and characterization of AlGaAs/GaAs heterojunctionbipolar transistors for high-temperature applications

The large signal dc characteristics of AlGaAs/GaAs heterojunction bipolar transistors (HBT) at high temperatures (27°-300°C) are reported. A high-temperature SPICE model is developed which includes the recombination-generation current components and avalanche multiplication which become extremely important at high temperatures. The effect of avalanche breakdown is also included to model the current due to thermal generation of electron/hole pairs causing breakdown at high temperatures. A parameter extraction program is developed and used to extract the model parameters of HBT's at different temperatures. Fitting functions for the model parameters as a function of temperature are developed. These parameters are then used in the SPICE Ebers-Moll model for the dc characterization of the HBT at any temperature between (27°-300°C)