Sensor placement for diagnosability

The concept of diagnostic accuracy is examined and redefined to support specific criteria for sensor placement. If the correctness of diagnoser operation is assumed, then any failure to diagnose accurately must be attributable to an inadequacy of sensor data. Inaccuracy in diagnoses can be expressed solely in terms of additional candidates whose faults cannot be ruled out. With ambiguity as the determiner of the quality of a diagnosis, user-defined diagnosability requirements can be expressed in terms of the types and instances of components which are permissible exceptions to perfect diagnosis. This requires a working diagnoser and a simulator, along with sets of system configurations, component fault modes, potentially measurable parameters, and uniqueness requirements for fault isolation. From these, the diagnosability of individual components can be determined for a particular attached subset of the available sensors. An optimum sensor assignment is one that satisfies the most requirements with a fixed number of sensors or, conversely, that minimizes the sensor requirements to achieve a given threshold of diagnosability. The considerable complexity of this search is reduced by exploiting sensor set minimality, structural knowledge, and diagnosis-free extension to the system level. Global optimization and sensor allocation do not add to the number of diagnoses required for diagnosability analysis. Finally, corrective measures are discussed for use when residual costs remain too high, or when redundancy is too low.In support of NASA's Marshall Space Flight Center and the Space Station Freedom Advanced Development Program under NASA contract number NAS 8-37200.     

Epoxy paint failure in B-52 fuel tanks: Part II. Influence of DIEGME concentration in the fuel on the failure process

A model has been proposed to explain the failure of the original BMS10-39 epoxy paint on upper vertical surfaces in B-52 fuel tanks. The model involves interaction of the paint with DIEGME, a fuel system ice inhibitor (FSII) in jet fuel, that is distilled from the liquid fuel. In this communication, distillation experiments used to support the model are refined to better match the mass transfer of vapor from fuel in a B-52 fuel tank at close to room temperature. The interaction of these lower temperature distillates with the paint affirms the earlier model. On the basis of these experiments it is proposed that paint failure may be controlled or eliminated by reducing the level of DIEGME in the fuel. Proposed changes in military jet fuel composition are detailed.     

The role of benchmarking for yardstick competition

With the increasing interest in yardstick regulation, there is a need to understand the most appropriate method for realigning tariffs at the outset. Benchmarking is the tool used for such realignment and is therefore a necessary first-step in the implementation of yardstick competition. A number of concerns have been raised about the application of benchmarking, making some practitioners reluctant to move towards yardstick based regimes. We assess five of the key concerns often discussed and find that, in general, these are not as great as perceived. The assessment is based on economic principles and experiences with applying benchmarking to regulated sectors, e.g. in the electricity and water industries in the UK, The Netherlands, Austria and Germany in recent years. The aim is to demonstrate that clarity on the role of benchmarking reduces the concern about its application in different regulatory regimes. We find that benchmarking can be used in regulatory settlements, although the range of possible benchmarking approaches that are appropriate will be small for any individual regulatory question. Benchmarking is feasible as total cost measures and environmental factors are better defined in practice than is commonly appreciated and collusion is unlikely to occur in environments with more than 2 or 3 firms (where shareholders have a role in monitoring and rewarding performance). Furthermore, any concern about companies under-recovering costs is a matter to be determined through the regulatory settlement and does not affect the case for using benchmarking as part of that settlement.     

Cost-effectiveness of preoperative localization studies in primary hyperparathyroid disease

OBJECTIVE: To evaluate the effect of preoperative localization studies on the surgical management of patients with primary hyperparathyroid disease (PHPT). SUMMARY BACKGROUND DATA: Reported cure rates of initial surgical exploration for PHPT are close to 95%. Preoperative localization studies are frequently obtained to improve surgical success and decrease operative time. METHODS: Initial cervical exploration was performed in 113 patients with PHPT from 1981 to 1993. Twenty-four patients (21%) had surgery without preoperative localization studies. The remaining 89 patients (79%) had 132 noninvasive preoperative localization studies. Success of the localization studies in tumor localization, pathologic findings, postoperative serum calcium levels, and operative times were compared. Patient costs of the studies were calculated. RESULTS: Disease was identified during operation in 23 of 24 patients (96%) having cervical exploration without preoperative localization studies, and they had normal calcium levels after surgery. Eighty-seven of 89 patients (98%) having preoperative localization studies were surgically cured. The highest sensitivity rate (60%) and highest positive predictive value (79%) of the localization studies were found with thallium-technetium scintiscanning. Average cost of the localization studies was $901 per patient. Combination studies were obtained in 32 patients at an average cost of $1,314 per patient without improving sensitivity. Mean operating time did not differ for localized and nonlocalized patients. CONCLUSIONS: Preoperative localization studies did not improve parathyroid localization or cure rate and did not substantially shorten operating time in initial cervical exploration for PHPT. The economic burden of routine preoperative localization studies in these patients is not justified.     

A monomial-based method for solving systems of non-linear algebraic equations

A monomial-based method for solving systems of algebraic non-linear equations is presented. The method uses the arithmetic-geometric mean inequality to construct a system of monomial equations that approximates the system of non-linear equations. A change of variables transforms the monomial system into a system of linear equations, which is readily solved. Special properties of the monomial method are identified and their significance is discussed. Invariance properties of the monomial method produce a built-in, self-adjusting scaling of the variables and equilibration of the equations of the linear system. Other special properties can lead to useful bounds on, and invariances of, the conditioning of the linear system. An invariance to uniform scaling is responsible for extremely rapid convergence to the equation surfaces in the initial iterations. An invariance to multiplication of the algebraic equations by a certain class of functions leads to a useful insensitivity to form of the algebraic system. Insensitivity of the monomial method to solutions with negative components avoids meaningless solutiuons of the algebraic system that appear as undesirable by-products of the formulation. A practical engineering design problem is solved to demonstrate the special properties of the monomial method.     

Electro‐optical transfer function preferences for LCD TVs: The effect of display brightness and surround illumination on preferred gamma

Abstract— Recent commercial liquid‐crystal‐display (LCD) televisions are larger and brighter than traditional televisions, thus impacting the viewing conditions in which they are viewed. These changes in viewing conditions may require different electro‐optical transfer functions (EOTFs) for LCD TVs than those for conventional TVs. Here, the way various EOTFs affect the preferred image quality of test images with changes in brightness and surround illumination conditions are examined. The first method used a gain, offset, and gamma (GOG) function with a range of gamma values, and the second method altered the intrinsic EOTFs. Image preference for the simulated EOTFs was determined using a paired‐comparison experiment for ten images. The first experiment took place in a darkened room at two display luminance levels. The results indicated that a gamma of 1.6 was most preferred overall although more so at a lower screen luminance level. In a second experiment, the procedure was repeated with a dim surround of 10% of the display's white point. With this surround, preference for a gamma value of around 1.6 at both screen luminance levels was more enhanced. These results indicated that image preference for different EOTFs is dependent on display luminance and that this dependence is maintained with a dim surround.     

Jitter reduction through feedback for picosecond pulsed InGaAsPlasers

Following a comparison of picosecond-pulse generation techniques, feedback schemes are reported for the generation of picosecond pulse trains with improved jitter for both multicontact and conventional single-contact InGaAsP-InP lasers. Subpicosecond jitter is achieved for Q-switched laser sources using a novel optoelectronic feedback scheme. The use of resonant electrical feedback is shown to improve the timing jitter of gain-switched pulses by up to six times. Pulse-to-pulse timing jitter as low as 250 fs is demonstrated for a hybrid of optical and electrical feedback schemes. Limits for timing jitter in diode lasers are established for optoelectronic, electrical, and optical feedback schemes, and the key picosecond pulse generation schemes are compared in terms of timing jitter for the first time     

Effect of molecular architecture on microstructural characteristics in some polysiloxaneimide multiblock copolymers

Efforts to correlate molecular characteristics with microstructural dimensions in microphase-separated diblock and triblock copolymers have been very successful, resulting in relationships that can be utilized to design materials with a specific microstructure and, consequently, with particular thermomechanical properties. However, similar efforts in the arena of multiblock copolymers have not been nearly as extensive, despite the increasing interest and diversity of this class of materials. In the present work, energy-filtered electron microscopy (EFEM) and small-angle neutron scattering (SANS) are used in a complementary fashion to probe the phase behavior of a series of three polysiloxaneimide (PSI) multiblock copolymers with different molecular architectures. Despite their relatively short segment lengths, all three materials exhibit signs of microphase separation at ambient temperature. SANS data are obtained from chemically unaltered materials and are subsequently interpreted with the Teubner-Strey model for microemulsions. Resultant microstructural dimensions are in good agreement with those measured from EFEM micrographs. Additional insight into the intramolecular sequencing of each copolymer is obtained from scaling relationships.     

Convection in a concentric annulus with heat generating porous media and a permeable inner boundary

The effects of a permeable inner boundary on the maximum temperature and the convective flows were investigated numerically for a two-dimensional horizontal annulus containing a uniformly heat generating porous media. The time-dependent governing equations were nondimensionalized and put into an explicit finite difference numerical form. The finite difference equations were obtained from truncated Taylor series expansions using a central differencing scheme. Nondimensional temperatures and streamlines were obtained for heat generation rates ranging from 20 to 1,500 W/m³ corresponding to a range of modified Rayleigh numbers of 324 to 24,340 and for several combinations of isothermally heated wall conditions for annuli of radius ratio of 2. It was found that multi-cellular flows occur at the highest Rayleigh numbers investigated.     

Do changes in cognitive factors influence outcome following multidisciplinary treatment for chronic pain? A cross-lagged panel analysis.

Changes in maladaptive cognitions may constitute therapeutic processes of multidisciplinary pain programs. A cross-lagged panel design was used to determine whether (a) early-treatment cognitive change predicted late-treatment outcome index change, but not vice versa; and (b) these effects remained significant with depression change controlled. Ninety chronic pain patients, in a 4-week multidisciplinary program, completed measures of catastrophizing, pain helplessness, depression, pain, interference, and activity level at pre-, mid-, and posttreatment. With depression changes controlled, early-treatment catastrophizing and pain helplessness changes predicted late-treatment outcome index changes, but not vice versa; early-treatment depression changes predicted late-treatment activity changes, but not vice versa. Findings advance understanding of pain treatment process and suggest that negative cognition changes may indeed affect improvements in treatment outcome. (PsycINFO Database Record (c) 2010 APA, all rights reserved)