Extended input-output models: progress and potential

"This article presents a critical survey of research on extended input-output models, emphasizing recent developments in demographic-economic and socio-economic analysis. Basic principles of model design and construction are reviewed, by reference to a representative selection of extended models. Two research themes--labor market analysis and income distribution--are pursued in greater detail as examples of the directions of current work. A comparison is made between extended models and social accounting matrices."     

Ontogenetic changes in pharyngeal morphology correlate with a diet shift from arthropods to dreissenid mussels in round gobies (Neogobius melanostomus)

The potential of predators to regulate populations of dreissenid mussels (Dreissena polymorpha and Dreissena rostriformis bugensis) has been addressed since early in the dreissenid invasion of North America. Round gobies (Neogobius melanostomus) larger than approximately 60 mm have been shown to prey extensively on dreissenids, whereas smaller round gobies feed mainly on aquatic insects and crustaceans. We propose that ontogenetic changes in pharyngeal morphology may contribute to this diet shift in round gobies. Pharyngeals of 69 round gobies ranging from 31 to 164 mm total length were investigated using light microscopy and scanning electron microscopy. Areas of lower pharyngeals and pharyngobranchial 2 increased allometrically with fish length. Pharyngeals of round gobies smaller than 50 mm contained narrow (< 0.1 mm diameter) papilliform teeth that are consistent with eating soft-bodied prey. By the time round gobies reached approximately 80 mm in length, pharyngeals contained larger diameter (0.3-0.5 mm) molariform teeth typical of those found in molluscivorous fish. Pharyngeal teeth of the largest round gobies also showed considerable wear. Although changes in pharyngeal morphology may contribute to the previously described diet shift in round gobies as they age, genetic and environmental factors both likely influence pharyngeal remodeling and therefore merit further investigation.     

The unanticipated difficult airway with recommendations for management

PURPOSE: To review the current literature and generate recommendations on the role of newer technology in the management of the unanticipated difficult airway. METHODS: A literature search using key words and filters of English language and English abstracted publications from 1990-96 contained in the Medline, Current Contents and Biological Abstracts databases was carried out. The literature was reviewed and condensed and a series of evidence-based recommendations were evolved. CONCLUSIONS: The unanticipated difficult airway occurs with a low but consistent incidence in anaesthesia practice. Difficult direct laryngoscopy occurs in 1.5-8.5% of general anaesthetics and difficult intubation occurs with a similar incidence. Failed intubation occurs in 0.13-0.3% general anaesthetics. Current techniques for predicting difficulty with laryngoscopy and intubation are sensitive, non-specific and have a low positive predictive value. Assessment techniques which utilize multiple characteristics to derive a risk factor tend to be more accurate predictors. Devices such as the laryngeal mask, lighted stylet and rigid fibreoptic laryngoscopes, in the setting of unanticipated difficult airway, are effective in establishing a patient airway, may reduce morbidity and are occasionally lifesaving. Evidence supports their use in this setting as either alternatives to facemask and bag ventilation, when it is inadequate to support oxygenation, or to the direct laryngoscope, when tracheal intubation has failed. Specifically, the laryngeal mask and Combitube have proved to be effective in establishing and maintaining a patent airway in "cannot ventilate" situations. The lighted stylet and Bullard (rigid) fibreoptic scope are effective in many instances where the direct laryngoscope has failed to facilitate tracheal intubation. The data also support integration of these devices into strategies to manage difficult airway as the new standard of care. Training programmes should ensure graduate physicians are trained in the use of these alternatives. Continuing medical education courses should allow physicians in practice the opportunity to train with these alternative devices.     

Domain flexibility in retroviral proteases: structural implications for drug resistant mutations

Rigid body rotation of five domains and movements within their interfacial joints provide a rational context for understanding why HIV protease mutations that arise in drug resistant strains are often spatially removed from the drug or substrate binding sites. Domain motions associated with substrate binding in the retroviral HIV-1 and SIV proteases are identified and characterized. These motions are in addition to closure of the flaps and result from rotations of approximately 6-7 degrees at primarily hydrophobic interfaces. A crystal structure of unliganded SIV protease (incorporating the point mutation Ser 4 His to stabilize the protease against autolysis) was determined to 2.0 A resolution in a new space group, P3221. The structure is in the most "open" conformation of any retroviral protease so far examined, with six residues of the flaps disordered. Comparison of this and unliganded HIV structures, with their respective liganded structures by difference distance matrixes identifies five domains of the protease dimer that move as rigid bodies against one another: one terminal domain encompassing the N- and C-terminal beta sheet of the dimer, two core domains containing the catalytic aspartic acids, and two flap domains. The two core domains rotate toward each other on substrate binding, reshaping the binding pocket. We therefore show that, for enzymes, mutations at interdomain interfaces that favor the unliganded form of the target active site will increase the off-rate of the inhibitor, allowing the substrate greater access for catalysis. This offers a mechanism of resistance to competitive inhibitors, especially when the forward enzymatic reaction rate exceeds the rate of substrate dissociation.     

Laser-speckle angular-displacement sensor: theoretical and experimental study

A novel, to our knowledge, method for the measurement of angular displacement for arbitrarily shaped objects is presented in which the angular displacement is perpendicular to the optical axis. The method is based on Fourier-transforming the scattered field from a single laser beam that illuminates the target. The angular distribution of the light field at the target is linearly mapped on a linear image sensor placed in the Fourier plane. Measuring this displacement facilitates the determination of the angular displacement of the target. It is demonstrated both theoretically and experimentally that the angular-displacement sensor is insensitive to object shape and target distance if the linear image sensor is placed in the Fourier plane. A straightforward procedure for positioning the image sensor in the Fourier plane is presented. Any transverse or longitudinal movement of the target will give rise to partial speckle decorrelation, but it will not affect the angular measurement. Furthermore, any change in the illuminating wavelength will not affect the angular measurements. Theoretically and experimentally it is shown that the method has a resolution of 0.3 mdeg ( approximately 5 murad) for small angular displacements, and methods for further improvement in resolution is discussed. No special surface treatment is required for surfaces giving rise to fully developed speckle. The effect of partially developed speckle is considered both theoretically and experimentally.     

Minimizing the average cost of paging and registration: A timer-based method

Methods of balancing call registration and paging are developed in this paper. Given that the probability distribution on the user location as a function of time is either known or can be calculated, previous work shows the existence of lower bounds on the average cost of paging. Here these bounds are used in conjunction with a Poisson incoming-call arrival model to formulate the paging/registration optimization problem in terms oftimeout parameters, _m ; the maximum amount of time to wait before registering given the last known location wasm. Timer-based methods, as opposed to location-based methods, do not require the user to record and process location information during the time between location updates. This feature might be desirable for minimizing mobile transceiver use during idle periods. We then consider uniform motion processes where a spatial translation of starting location produces an identical spatial translation of the associated time-varying probability distribution. This leads to a universal timeout parameter which may be readily calculated. We study and the minimum cost of paging/registration for a simple model of user motion and compare our results to an earlier method of location-based paging/registration cost minimization.     

A survey of problems,solution techniques,and future challenges in scheduling semiconductor manufacturing operations

In this paper, we discuss scheduling problems in semiconductor manufacturing. Starting from describing the manufacturing process, we identify typical scheduling problems found in semiconductor manufacturing systems. We describe batch scheduling problems, parallel machine scheduling problems, job shop scheduling problems, scheduling problems with auxiliary resources, multiple orders per job scheduling problems, and scheduling problems related to cluster tools. We also present important solution techniques that are used to solve these scheduling problems by means of specific examples, and report on known implementations. Finally, we summarize some of the challenges in scheduling semiconductor manufacturing operations.