Non-destructive evaluation of cement-based materials from pressure-stimulated electrical emission - Preliminary results

This is the post-print version of the final paper published in Construction and Building Materials. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.This paper introduces the possibility of in situ assessment of loading and remaining strength in concrete structures by means of measuring discharge of electric current from loaded specimens. The paper demonstrates that the techniques have been applied to other rock-like materials, but that for the first time they are applied to cement-based materials and a theoretical model is proposed in relation to the appearance of electrical signals during sample loading and up to fracture. A series of laboratory experiments on cement mortar specimens in simple uniaxial compression, and subsequently in bending – hence displaying both tension and compression – are described and show clear correlations between resulting strains and currents measured. Under uniaxial loading there is a well-defined relationship between the pressure-stimulated current (PSC) as a result of a monotonic mechanical loading regime. Similar results are observed in the three-point bending tests where a range of loading regimes is studied, including stepped changes in loading. While currents can be measured at low strains, best results seem to be obtained when strains approach and exceed yield stress values. This technique clearly has immense potential for structural health monitoring of cement-based structures. Both intermittent and continuous monitoring becomes possible, and given an ongoing campaign of monitoring, remaining strength can be estimated

Government Activism in Bankruptcy

It is widely recognized that bankruptcy law can stymie regulatory enforcement and present challenges for governments when regulated businesses file for Chapter 11. It is less-widely understood that bankruptcy law can present governments with opportunities to advance policy goals if they are willing to adopt tactics traditionally associated with activist investors, a strategy we call “government bankruptcy activism.” The bankruptcy filings by Chrysler and General Motors in 2009 are a famous example: the government of the United States used the bankruptcy process to help both auto manufacturers resolve their financial distress while promoting the policy objectives of protecting union workers and addressing climate change. A decade later, the government of California applied its bargaining power in the Pacific Gas & Electric Company’s Chapter 11 case to protect climate policies and the victims of wildfires. These examples illustrate that, by tapping into the bankruptcy system, governments gain access to the exceptional powers that a debtor enjoys under bankruptcy law, which can complement the traditional tools of appropriations and regulation to facilitate and accelerate policy outcomes. This strategy is especially useful in times of urgency and policy paralysis, when government bankruptcy activism can provide a pathway past veto players in the political system. However, making policy through the bankruptcy system presents potential downsides as well, as it may also allow governments to evade democratic accountability and obscure the financial losses that stakeholders are forced to absorb to help fund those policy outcomes

Towards a Reconfigurable Sense-and-Stimulate Neural Interface Generating Biphasic Interleaved Stimulus

Published versio

A CMOS Magnitude/Phase Measurement Chip for Impedance Spectroscopy

The measurement of electrical impedance is used in a plethora of biomedical applications. The most common technique used is synchronous demodulation, which provides the real and imaginary parts of the impedance. However, in practice, the method requires elaborate calibration and matching between the injection and monitoring stages. This paper presents the integrated realization of an alternative method that is less intricate to implement. The circuit was fabricated in a 0.35-μm CMOS technology, occupies an active area of 0.4 mm2 , and dissipates about 21 mW of power from ±2.5 V supplies. The chip was used to measure equivalent RC circuits of the electrode-tissue interface over the frequency range of 100 Hz to 100 kHz, showing good correlation with the theoretical results

Bankruptcy’s Uneasy Shift to a Contract Paradigm

The most dramatic development in twenty-first century bankruptcy practice has been the increasing use of contracts to shape the bankruptcy process. To explain the new contract paradigm—our principal objective in this Article-- we begin by examining the structure of current bankruptcy law. Although the Bankruptcy Code of 1978 has long been viewed as mandatory, its voting and cramdown rules, among others, invite considerable contracting. The emerging paradigm is asymmetric, however. While the Code and bankruptcy practice allow for ex post contracting, ex ante contracts are viewed with suspicion.We next use contract theory to assess the two modes of contracting. The principal benefit of ex post contracting stems from the parties’ inability to anticipate each possible future contingency. Whereas an ex ante contract faces the challenge of providing for many possible future states of the world, an ex post contract can provide for the one that materialized. Ex ante contracting also provides distinct benefits, however, even if it is incomplete. It can encourage reliance on investments by the parties, efficiently allocates risk, and establishes incentives. Given time-inconsistent preferences of the parties, the prospect of ex post contracting can prevent the parties from exploiting these benefits. Contract theory has shown that it is difficult in practice for parties to prevent renegotiation or otherwise avoid this outcome.We apply these insights to a number of key areas of current bankruptcy contracting including: the ex post contracts facilitated by the voting and confirmation rules of the Code itself; the use (and contrasting judicial treatment) of intercreditor and restructuring support agreements to contract around ostensibly mandatory Chapter 11 provisions; and substantive consolidation of the cases of a debtor and its affiliates. Even if all of the relevant parties consent, an ex post renegotiation may be inefficient if it undermines the parties’ ex ante arrangements. Yet, bankruptcy encourages such ex post contracting while discouraging ex ante attempts to avoid this outcome. We conclude that courts are too hostile to ex ante contracting, and they should subject ex post contracts to more careful review

Towards an optimized tetrapolar electrical impedance lithium detection probe for bipolar disorder: A simulation study

Bipolar disorder is characterized as a manic-depressive syndrome with severe risks to the individual. Bipolar patients' therapy involves administration of lithium which has proven to be effective for mood stabilization. The therapeutic concentration window for lithium in blood plasma is typically between 0.6-1.5 mM and is of vital importance that concentrations do not exceed the 1.5mM as it can be toxic. Accurate monitoring of the concentration changes of Lithium in blood, down to levels of approximately 0.2mM is vital since toxicity levels are in close proximity to therapeutic levels. This paper aims to study the sensitivity of tetrapolar electrical impedance measurements when used to monitor changes in the conductivity of a solution/sample as in the case of changes in Lithium concentration in blood

High-power CMOS current driver with accurate transconductance for electrical impedance tomography

Current drivers are fundamental circuits in bioimpedance measurements including electrical impedance tomography (EIT). In the case of EIT, the current driver is required to have a large output impedance to guarantee high current accuracy over a wide range of load impedance values. This paper presents an integrated current driver which meets these requirements and is capable of delivering large sinusoidal currents to the load. The current driver employs a differential architecture and negative feedback, the latter allowing the output current to be accurately set by the ratio of the input voltage to a resistor value. The circuit was fabricated in a 0.6-μ m high-voltage CMOS process technology and its core occupies a silicon area of 0.64 mm2. It operates from a ± 9 V power supply and can deliver output currents up to 5 mA p-p. The accuracy of the maximum output current is within 0.41% up to 500 kHz, reducing to 0.47% at 1 MHz with a total harmonic distortion of 0.69%. The output impedance is 665 kΩ at 100 kHz and 372 k Ω at 500 kHz