Showing papers on "NQS published in 1993"

Simultaneous identification of amphetamine and its derivatives in urine using HPLC-UV.

Abstract: An HPLC-UV method for the simultaneous identification of amphetamine, methamphetamine, 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxymethamphetamine (MDMA) in urine is described. It includes a rapid extraction procedure of the 4 analogs from urine using Extrelut 3 columns, derivatization with sodium 1,2-naphthoquinone-4-sulphonate (NQS) to obtain highly chromophoric UV-VIS derivatives, and a final HPLC analysis using an ion-pair reversed-phase technique with eluent monitoring at 480 nm. Structural characterization of the derivatives obtained by mass spectrometry is reported. Recoveries of the amphetamines were in the range 80–85% at concentrations of 300 ng/ml. Practical detection limits were 40–60 ng/ml (S/N ratio = 10) for all derivatives. The chromatographic peaks of the NQS derivatized amphetamines are fairly narrow and well resolved. The method is simple, rapid, quite sensitive, and specific for convenient confirmation of preliminary positive results obtained with immunoassays.

An investigation into the nonquasistatic effects in MOS devices with on-wafer S-parameter techniques

Abstract: The high-frequency characteristics of MOS devices are investigated with a view to the identification of nonquasistatic (NQS) effects considering the Bagheri and Tsividis I-order NQS model as a reference. An exhaustive set of data is analyzed. It indicates the existence of NQS effects in long- as well as short-channel devices. Significant differences are observed between a charge based quasi-static model and measurements for a long-channel (25- mu m) device. A deembedding technique is suggested to observe the intrinsic device behavior up to a higher range of frequencies. >

Benzoic acid determination through competitive inhibition of mediated bioelectrocatalysis

Abstract: A bioelectrochemical system for the sensing of benzoic acid is described. An enzyme-based oxygen electrode is constructed where the enzymatic consumption of oxygen by tyrosinase is monitored electrochemically through the mediator 1,2 naphthoquinone, 4-sulfonate (NQS). The bioelectrocatalysis of oxygen can be electrochemically initiated and terminated and is sensitive to inhibition by benzoic acid in a concentration-dependent manner. Inhibition of catalytic current results from a competitive interaction of benzoic acid at the enzymatic docking site of NQS. This inhibition of catalytic activity is reversible, and full catalytic activity can be reinstated following the removal of benzoic acid from solution. The sensing of benzoic acid is dependent on the nature of the mediator used, occurring with NQS but not with ferricyanide. These studies provide support for the possibility that analytes can be targeted for detection in such inhibition-based sensing through the proper selection of mediator.

Automatic Checkpointing of NQS Batch Jobs on CRAY UNICOS Systems

Abstract: In most UNIX systems long running application programs are not protected against the loss of their accumulated CPU time in case of regular shutdowns or system crashes. In contrast to these systems, the UNICOS operating system provides a checkpoint/restart facility, which allows e.g. to recover NQS batch jobs after a regular system shutdown and reboot. However, there is still no function, which periodically performs checkpointing of running processes. This kind of checkpointing, which would minimize CPU time losses in case of system crashes, is completely left to the user. Unfortunately, most of the users do not care about checkpointing. Therefore, a feature was developed at KFA, allowing to checkpoint NQS batch jobs automatically after a certain CPU time interval. The key issue of this feature is a UNIX daemon which is activated together with each NQS request. We present a detailed description of the daemon and its user interface. Our experience in a production environment shows, that the CPU time losses due to system crashes can be drastically reduced by this feature.

Non-quasi-static effects in advanced high-speed bipolar circuits

Abstract: A detailed study on the non-quasi-state (NQS) effects in advanced high-speed bipolar circuits is presented. An NQS Gummel-Poon-compatible lumped circuit model, which accounts for carrier propagation delays across various quasi-neutral regions in bipolar devices, is implemented in the ASTAP circuit simulator. The effects are then evaluated and compared with those for the conventional Gummel-Poon model for the emitter-coupled logic (ECL) circuit, the non-threshold-logic (NTL) circuit, and various advanced circuits utilizing active-pull-down schemes. For the ECL circuit, the effect decreases with reduced power level and increased loading. For the NTL circuit, due to its front-end configuration, the effect is more significant than that for the ECL circuit but tends to increase with reduced power level. As the passive resistors (and the associated parasitic RC effect) are decoupled from the delay path and the circuit delay is made more intimately related to the intrinsic speed of the devices in various advanced active-pull-down circuits, the delay degradation due to NQS effect becomes more significant. >

An Efficient Non-Quasi-Static Diode Model for Circuit Simulation

Abstract: Based on the partitioned-charge-based modeling approach, a general non-quasi-static dynamic charge element is derived to simulate both transient behavior and high-frequency characteristics of a semiconductor diode. A new model parameter [tau] is introduced to describe the dynamic charge redistribution time for a diode, and can be determined based on an extraction method proposed. By partitioning the total base charge into quasi-static (QS) and non-quasi-static (NQS) terms, a single-t (level 2) diode model is first derived. By further dividing the NQS charge, a double-t (level 3) diode model is proposed to describe different reverse recovery processes. In addition, a voltage-dependent equation is incorporated to the double-t model to account for the dynamic charge partitioning. We show that the SPICE diode (level-1) model is included by setting t to zero as a special case of the proposed models. The new diode model has been verified in MISIM, a Model Independent SPICE-like SIMulation framework. Significant improvement in accuracy over the traditional SPICE diode model in both time and frequency domain has been demonstrated, while achieving the same or even better simulation speed and reliability.

A comprehensive non-quasi-static capacitance model for graded heterojunction bipolar transistors

Abstract: A new non-quasi-static (NQS) capacitance model for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is presented. This model takes into consideration the effects of Al-composition variation, free carriers in the space-charge region (SCR), and NQS delay in the device. The results show how the grading can influence the SCR width, the electric field, the electron charge density, and the junction capacitance values. The computation results obtained from the present model are compared with the results obtained from Anderson's and Liou's models. It can be concluded, from these results, that this model can predict the values of capacitance parameters more accurately than other existing capacitance models.

A non-quasi-static modular model for HBTs

Abstract: Heterojunction bipolar transistors (HBTs) show promise as a high speed and high power density device for many circuit applications. However the quasi-static models found in standard circuit simulation tools can not treat fast transients in HBTs properly. This leads to inaccurate simulations at high frequency and of strongly non-linear operation. To properly account for the charge in transit through the device, non-quasi-static (NQS) models must be used. This work presents a model for the bipolar transistor formed from regional modules. Each module is a NQS solution to a specific region of the transistor and uses material and geometry inputs. These modules are solved for physical consistency during non-linear circuit simulation. The modularization allows appropriate approximations for each region to yield analytic solutions. The input parameters for the model reflect the physical structure of the device as much as possible to provide intuitive results and verifiability. This allows direct device optimization since all parameters are either uncorrelated or their correlations can be derived from process parameters. Thus the device can be optimized in its circuit environment. The model provides for many effects which previously required numerical simulation for accurate results. These include forward and reverse Early, Webster/Rittner, and Kirk/quasisaturation effects. By following the modular modeling scheme, these effects are simply the result of varying boundary conditions on each of the regional solutions. The modular model provides much of the physical insight of numerical models but with computational requirements on the same order as conventional circuit models. >

Non-quasi-static effects in saturated bipolar circuits

Abstract: A non-quasi-static (NQS) model accounting for intrinsic carrier propagation delays in both B/E and B/C junctions is implemented in the ASTAP circuit simulator to evaluate the impact of non-quasi-static effects in saturated bipolar circuits. It is shown that while the extra delay introduced by the NQS effects during the turn-on transition is primarily due to the normal mode B/E NQS time constant, the more severe NQS delay in the turn-off transition is caused mainly by the removal of the saturation over-drive charges and the longer inverse mode B/C NQS time constant. >