Exponential lower bounds for depth three Boolean circuits

We consider the class of unbounded fan-in depth three Boolean circuits, for which the bottom fan-in is limited by k and the top gate is an OR. It is known that the smallest such circuit computing the parity function has gates (for k = O(n ^1/2)) for some , and this was the best lower bound known for explicit (P-time computable) functions. In this paper, for k = 2, we exhibit functions in uniform NC ¹ that require size depth 3 circuits. The main tool is a theorem that shows that any circuit on n variables that accepts a inputs and has size s must be constant on a projection (subset defined by equations of the form x _i = 0, x _i = 1, x _i = x _j or x _i = ) of dimension at least log(a/s)log n. Received: April 1, 1997.     

Flow and crystallization of saturated fatty acid methyl esters and their binary mixtures

Demand for biodiesel has increased due to being a more environmentally-friendly fuel. Cold weather operation of biodiesel is challenging due to fatty acid methyl ester (FAME) content in biodiesel. Saturated FAMEs crystallize at relatively high temperatures, increase the viscosity of biodiesel, and can clog fuel lines. Here, several factors altered crystallization temperature (CT) of FAMEs, including composition, shear rate, and cooling rate. The crystallization of pure and binary mixtures of methyl palmitate, methyl myristate, and methyl stearate were studied under shear flow and static conditions. Static phase CTs of pure methyl palmitate, methyl myristate, and methyl stearate were 26, 14, and 35°C, respectively. In binary mixtures, CTs were depressed up to 7°C, which agreed with freezing point depression theory. Increasing shear rate up to 100 s⁻¹ decreased CT by 2°C compared to static conditions. Decreasing cooling rate from 1 to 0.1°C/min increased CT less than 2°C. Overall, FAME composition altered CT more than shear flow or cooling rate for pure and binary mixtures of three FAMEs.     

Overview and Lessons from More Than a Decade of Feeder Life Management

This paper provides an overview of the degradation in CANDU~a （Canadian Deuterium Uranium） feeders in operating plants observed from the mid 1990s onward. The degradation has been dominated by feeder wall thinning, caused by FAC （flow accelerated corrosion） and feeder cracking. This paper summarizes the industry＇s response to the discovery of these two degradation mechanisms and the methodologies, tools and technologies developed to monitor the degradation and assess the continued fitness for service to manage the plant life. This paper identifies some of the lessons gained from more than a decade of industry effort, and discusses how these lessons are being implemented in the refurbished and new CANDU plants. CANDU~a is a registered trademark of Atomic Energy of Canada Limited.     

Consistent low-field picture of bcc3He exchange

Consideration of a physically plausible potential for bcc solid³He suggests that there is significant antiferromagnetic pair exchange between next nearest neighbors and that triple exchange is less important than previously believed. Experimental consequences of such a thesis are consistent with all existing low magnetic field data.     

Low Frequency Architecture for Multi-Lamp CCFL Systems With Capacitive Ignition

A low frequency architecture is proposed for driving parallel cold cathode fluorescent lamps (CCFLs) in large screen liquid crystal display (LCD) TV backlighting applications. Key to the architecture is a proposed capacitive coupling approach for aiding lamp ignition. A dc voltage is applied to the lamp electrodes while an ac voltage is applied to an external plate for capacitive coupling. The result is reliable, simultaneous ignition of parallel lamps with a required applied dc voltage near the lamp steady-state operating voltage. The complete system architecture includes a single high voltage converter, a pulse lamp ignition circuit, current control circuits and a single backlight controller. The topology is capable of driving a large number of parallel lamps with independent lamp current regulation, while avoiding ac coupling losses in steady-state operation and achieving significant reduction in reactive components when compared to typical high frequency ac ballast designs. Experimental results are presented for a system of four parallel 250 mm length lamps, demonstrating simultaneous parallel lamp ignition and dc current regulation.     

Clinical evidence framework for Bayesian networks

There is poor uptake of prognostic decision support models by clinicians regardless of their accuracy. There is evidence that this results from doubts about the basis of the model as the evidence behind clinical models is often not clear to anyone other than their developers. In this paper, we propose a framework for representing the evidence-base of a Bayesian network (BN) decision support model. The aim of this evidence framework is to be able to present all the clinical evidence alongside the BN itself. The evidence framework is capable of presenting supporting and conflicting evidence, and evidence associated with relevant but excluded factors. It also allows the completeness of the evidence to be queried. We illustrate this framework using a BN that has been previously developed to predict acute traumatic coagulopathy, a potentially fatal disorder of blood clotting, at early stages of trauma care.     

Online calibration of MOSFET on-state resistance for precise current sensing

An approach for online current sensing calibration is presented where an auxiliary switch and a precision sense resistor are connected in parallel with a main power switch to achieve accuracy comparable to the sense resistor method, together with the advantage of essentially no additional power loss. The proposed current-sensing circuit and the calibration methods are particularly well suited for digital controller implementations where the required control and calibration functions can be easily accomplished. Experimental results with a digitally controlled 1.5-V 15-A synchronous buck converter demonstrate functionality of the online calibration approach, showing a significant improvement in accuracy over voltage sensing across the power MOSFET on-resistance.     

Effect of calixpyrrole in PEO-LiBF4 polymer electrolytes

It is shown that the addition of calix[6]pyrrole to polyether based electrolytes doped with LiBF₄ results in an considerable increase in the cation transport number tLi+ as confirmed by dc-ac current techniques as well as by PFG NMR studies. The value of tLi+ in composite electrolytes beyond a certain minimum value weakly depends on the concentration of added calix[6]pyrrole. The increase in lithium transference number is associated with a decrease in ionic conductivity of composite polymeric electrolytes compared to the pure PEO-LiBF₄ systems.     

Thermosetting polymers in cold sintering: The fabrication of ZnO-polydimethylsiloxane composites

This study reports the fabrication of the first ceramics-thermosetting polymer composites by the cold sintering process, for high ceramic volume fractions (v/v >95%). The (1 − x) ZnO − x polydimethylsiloxane (PDMS) composites, with 0.00 ≤ x ≤ 0.05, were cold sintered at 250°C, 320 MPa for 60 minutes. In situ densification studies conducted with the help of a semi-automated press revealed that the mechanisms driving the densification of the material changes with the polymer content. Relative densities of the (1 − x) ZnO − x PDMS composites (0.00 ≤ x ≤ 0.05) were above 90%. Impedance spectroscopy of the composites yields insight into the ceramic-polymer interfaces within the sintered ZnO bulk and suggests long-range conduction governed by ZnO-PDMS interface properties for x = 0.03 and x = 0.05. The study also emphasizes on the complexities and opportunities of such ceramic-dominated ceramic-polymer composites.