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Statement of problem Although in vitro studies have investigated the accuracy of virtual interocclusal records, clinical research on their ability to register virtual dental casts accurately is lacking. Purpose The purpose of this clinical study was to evaluate the accuracy and reproducibility of the virtual interocclusal records of an intraoral scanning system compared with conventional polyvinyl siloxane (PVS) interocclusal records. Material and methods Three conventional interocclusal records followed by 3 virtual interocclusal records per side per participant were made in 10 participants. Three sites of close proximity (SCP) and 3 sites of clearance (SC) per side per participant were identified on the transilluminated conventional interocclusal PVS records for a total of 60 SCP and SC. The presence or absence of these sites on the virtual interocclusal records was analyzed by using an independent software program. Results The sensitivity for correct identification in the virtual interocclusal record was 87%, and its specificity was 95%. The positive predictive value was 95%, and the negative predictive value was 88%. For reproducibility, 74% of the SCP were detected consistently for all 3 repeated scans, and 92% of the SCs were identified accurately. Conclusions The accuracy of virtual interocclusal records in identifying interocclusal contacts is clinically acceptable. However, the method tends to miss interocclusal contacts rather than introducing false ones and can result in perforations between the opposing virtual casts. Repeated buccal occlusal scans made of the same side showed fair reproducibility, and this aspect would benefit from further investigation.

Contact investigation is one public health measure used to prevent tuberculosis by identifying and treating persons exposed to Mycobacterium tuberculosis. Contact investigations are a major tenet of global tuberculosis elimination efforts, but for many reasons remain ineffective. We describe a novel neighbor-based approach to reframe contact investigations.

Background: In a spatially well known and dispersed HIV epidemic, identifying geographic clusters with significantly higher HIV prevalence is important for focusing interventions for people living with HIV (PLHIV). Methods: We used Kulldorff spatial-scan Poisson model to identify clusters with high numbers of HIV-infected persons 15–64 years old. We classified PLHIV as belonging to either higher prevalence or lower prevalence (HP/LP) clusters, then assessed distributions of sociodemographic and biobehavioral HIV risk factors and associations with clustering. Results: About half of survey locations, 112/238 (47%) had high rates of HIV (HP clusters), with 1.1–4.6 times greater PLHIV adults observed than expected. Richer persons compared with respondents in lowest wealth index had higher odds of belonging to a HP cluster, adjusted odds ratio (aOR) 1.61 [95% confidence interval (CI): 1.13 to 2.3], aOR 1.66 (95% CI: 1.09 to 2.53), aOR 3.2 (95% CI: 1.82 to 5.65), and aOR 2.28 (95% CI: 1.09 to 4.78) in second, middle, fourth, and highest quintiles, respectively. Respondents who perceived themselves to have greater HIV risk or were already HIV-infected had higher odds of belonging to a HP cluster, aOR 1.96 (95% CI: 1.13 to 3.4) and aOR 5.51 (95% CI: 2.42 to 12.55), respectively; compared with perceived low risk. Men who had ever been clients of female sex worker had higher odds of belonging to a HP cluster than those who had never been, aOR 1.47 (95% CI: 1.04 to 2.08); and uncircumcised men vs circumcised, aOR 3.2 (95% CI: 1.74 to 5.8). Conclusions: HIV infection in Kenya exhibits localized geographic clustering associated with sociodemographic and behavioral factors, suggesting disproportionate exposure to higher HIV risk. Identification of these clusters reveals the right places for targeting priority-tailored HIV interventions.

During 2012–2015, 10 of 24 patients infected with matching genotypes of Mycobacterium tuberculosis received care at the same hospital in Gaborone, Botswana. Nosocomial transmission was initially suspected, but we discovered plausible sites of community transmission for 20 (95%) of 21 interviewed patients. Active case-finding at these sites could halt ongoing transmission.

The voice is a unique characteristic that we use to identify one another – including someone's sex, age and mood. We speak by using air flow to vibrate our vocal folds, commonly known as vocal cords. The land-living ancestors of the African clawed frog Xenopus also used breath and vocal cords to communicate, but they returned to aquatic life 180 million years ago and had to evolve a different way to create sounds. Today’s Xenopus live in water and use a new mechanism that lets them sing for hours underwater without coming up to breathe. Males from each major group of Xenopus species produce courtship songs with harmonic intervals corresponding to an octave, a perfect fourth, or a major or minor third. Today's Xenopus species do not have any vocal cords. Instead, they have an elaborate set of vocal components: the muscles of the larynx contract paired, movable rods that end in discs. For the past 40 years, it was thought that these frogs create sounds by collapsing small air bubbles between the discs, similar to snapping shrimp. But such bubbles have never been observed, and exactly how these frogs manage to create sounds underwater has been a mystery. Here, Kwong-Brown et al. filmed the larynx as it was stimulated to produce sounds and discovered that the rapid separation of the discs excites the larynx and the surrounding tissues to create the harmonic frequencies. Then, to determine how the frog creates its harmonic intervals, Kwong-Brown et al. tried to ‘detune’ the larynx. In a series of experiments, they placed weights on the surface of the larynx, drilled a hole in the cartilage and filled it with helium, or introduced small glass beads. None of these attempts had any effect. However, rupturing the elastic cartilages within the larynx – which separate its internal cavity into three chambers – disrupted the harmonic intervals. This new way of creating underwater sounds helped to maintain the quality of the frog’s voice and may explain how Xenopus can shape its songs to convey crucial information to others, such as identifying species, sex and social intent.

Time-constant assumptions in discrete-response heterogeneity models can often be violated. To address this, a time-varying heterogeneity approach to model unobserved heterogeneity in ordered response data is considered. A Markov switching random parameters structure (which accounts for heterogeneity across observations) is proposed to accommodate both time-varying and time-constant (cross-sectional) unobserved heterogeneity in an ordered discrete-response probability model. A data augmented Markov Chain Monte Carlo algorithm for non-linear model estimation is developed to facilitate model estimation. The performance of the cross-sectional heterogeneity model and time-varying heterogeneity model are examined with vehicle crash-injury severity data. The time-varying heterogeneity model (Markov switching random parameters ordered probit) is found to provide the best overall model fit. Two roadway safety states are shown to exist and roadway segments transition between these two states according to Markov transition probabilities. The results demonstrate considerable promise for Markov switching models in a wide variety of applications.

Background: Since 2004, several African countries, including Namibia, have received assistance from the U.S. President's Emergency Plan for AIDS Relief (PEPFAR). Aims: Gains have been documented in the safety and number of collected units in these countries, but the distribution of blood has not been described. Methods: Nine years of data on blood requests and issues from Namibia were stratified by region to describe temporal and spatial changes in the number and type of blood components issued to Namibian healthcare facilities nationally. Results: Between 2004-2007 (early years of PEPFAR support) and 2008-2011 (peak years of PEPFAR support), the average number of red cell units issued annually increased by 23.5% in seven densely populated but less developed regions in northern Namibia; by 30% in two regions with urban centers; and by 35.1% in four sparsely-populated rural regions. Summary/Conclusions: Investments in blood safety and a policy decision to emphasize distribution of blood to underserved regions improved blood availability in remote rural areas and increased the proportion of units distributed as components. However, disparities persist in the distribution of blood between Namibia's urban and rural regions.

The United States is experiencing a major public health problem relating to increasing levels of excess body fat. This paper is about the relationship in the United States between trends in the distribution of body mass index (BMI), including trends in overweight and obesity, and demographic change. We provide estimates of the counterfactual distribution of BMI that would have been observed in 2003–2008 had demographics remained fixed at 1980 values, roughly the beginning of the period of increasing overweight and obesity. We find that changes in demographics are partly responsible for the changes in the population distribution of BMI and are capable of explaining about 8.6% of the increase in the combined rate of overweight and obesity among women and about 7.2% of the increase among men. We also use demographic projections to predict a BMI distribution and corresponding rates of overweight and obesity for 2050.

A comprehensive model stitching simulation architecture has been developed, which allows continuous, full flight-envelope simulation based on a collection of discrete-point linear models and trim data. The model stitching simulation architecture is applicable to any aircraft configuration readily modeled by state equations and for which test data can be obtained. Individual linear models and trim data for specific flight conditions are incorporated with nonlinear elements to produce a continuous, quasi-nonlinear simulation model. Extrapolation methods within the model stitching architecture permit accurate simulation of off-nominal aircraft loading configurations, including variations in weight, inertia, and center of gravity, and variations in altitude, which together minimize the required number of point models for full-envelope simulation. The model stitching simulation architecture is applied herein to a model of a CJ1 business jet and to a model of a UH-60 utility helicopter. For both the fixed-wing and the rotorcraft application, configuring the stitched simulation models with 8 discrete-point linear models (4 point models each at two altitudes) plus additional trim data was found to allow accurate simulation over the full airspeed and altitude envelope. Flight-test implications for the development of stitched models from flight-identified point models are presented for fixed-wing and rotorcraft applications.

Introduction Using spatial–temporal analyses to understand coverage and trends in elimination of mother-to-child transmission of HIV (e-MTCT) efforts may be helpful in ensuring timely services are delivered to the right place. We present spatial–temporal analysis of seven years of HIV early infant diagnosis (EID) data collected from 12 districts in western Kenya from January 2007 to November 2013, during pre-Option B+ use. Methods We included in the analysis infants up to one year old. We performed trend analysis using extended Cochran–Mantel–Haenszel stratified test and logistic regression models to examine trends and associations of infant HIV status at first diagnosis with: early diagnosis ( Results Median age was two months, interquartile range 1.5–5.8 months. Unadjusted pooled positive rate was 11.8% in the seven-years period and declined from 19.7% in 2007 to 7.0% in 2013, p < 0.01. Uptake of testing ≤8 weeks after birth was under 50% in 2007 and increased to 64.1% by 2013, p < 0.01. By 2013, the overall standardized MTCT rate was 447 infections per 100,000 live births. Based on Bayesian deviance information criterion comparisons, the spatial–temporal model with maternal and infant covariates was best in explaining geographical variation in MTCT. Discussion Improved EID uptake and reduced MTCT rates are indicators of progress towards e-MTCT. Cojoined analysis of time and covariates in a spatial context provides a robust approach for explaining differences in programmatic impact over time. Conclusion During this pre-Option B+ period, the prevention of mother to child transmission program in this region has not achieved e-MTCT target of ≤50 infections per 100,000 live births. Geographical disparities in program achievements may signify gaps in spatial distribution of e-MTCT efforts and could indicate areas needing further resources and interventions.

Use of the Louisiana Immunization Network for Kids Statewide (LINKS) during the aftermath of Hurricane Katrina saved parents and immunization providers' time, money, and the inconvenience of having to unnecessarily revaccinate children displaced both inside and outside Louisiana. This immunization information system remained online via a backup system following the hurricane, thereby making immunization history data available to queries from healthcare providers caring for displaced persons both within Louisiana and throughout the United States. LINKS contained immunization records for approximately 1.5 million people of all ages at the time of the hurricane. Assessment of more than 21 000 successful electronic immunization queries of children and adolescents displaced outside Louisiana state boundaries from virtually all states estimates that more than $4.6 million was saved in revaccination expenses. The impact of recovered records for these children within Louisiana is certainly as critical. Our review illustrates the value of an immunization information system as a tool to support not only individuals, healthcare providers, and public health authorities but also the presidential vision to develop Electronic Health Records in the United States over the next 10 years.

Background and Objectives Since 2004, several African countries, including Namibia, have received assistance from the U.S. President's Emergency Plan for AIDS Relief (PEPFAR). Gains have been documented in the safety and number of collected units in these countries, but the distribution of blood has not been described. Materials and Methods Nine years of data on blood requests and issues from Namibia were stratified by region to describe temporal and spatial changes in the number and type of blood components issued to Namibian healthcare facilities nationally. Results Between 2004 and 2007 (early years of PEPFAR support) and 2008–2011 (peak years of PEPFAR support), the average number of red cell units issued annually increased by 23.5% in seven densely populated but less-developed regions in northern Namibia; by 30% in two regions with urban centres; and by 35.1% in four sparsely populated rural regions. Conclusion Investments in blood safety and a policy decision to emphasize distribution of blood to underserved regions improved blood availability in remote rural areas and increased the proportion of units distributed as components. However, disparities persist in the distribution of blood between Namibia's urban and rural regions.

This study focuses on the role of male-male vocal communication in the reproductive repertoire of the South African clawed frog, Xenopus laevis. Six male and two female call types were recorded from native ponds in the environs of Cape Town, South Africa. These include all call types previously recorded in the laboratory as well as one previously unidentified male call: chirping. The amount of calling and the number of call types increased as the breeding season progressed. Laboratory recordings indicated that all six male call types were directed to males; three of these were directed to both sexes and three were directed exclusively to males. Both female call types were directed exclusively to males. The predominant call type, in both field and laboratory recordings, was the male advertisement call. Sexual state affected male vocal behaviour. Male pairs in which at least one male was sexually active (gonadotropin injected) produced all call types, whereas pairs of uninjected males rarely called. Some call types were strongly associated with a specific behaviour and others were not. Clasped males always growled and clasping males typically produced amplectant calls or chirps; males not engaged in clasping most frequently advertised. The amount of advertising produced by one male was profoundly affected by the presence of another male. Pairing two sexually active males resulted in suppression of advertisement calling in one; suppression was released when males were isolated after pairing. Vocal dominance was achieved even in the absence of physical contact (clasping). We suggest that X. laevis males gain a reproductive advantage by competing for advertisement privileges and by vocally suppressing neighbouring males.

In this paper I explore the relationship between ability and log waves using flexible estimation techniques. I find evidence of nonlinearities in these relationships that vary across levels of schooling, and argue that ability-sorting into higher education creates problems for accurately identifying the return to schooling over the entire ability support. Over an ability support that is “common” to those with and without a college education, I find that the college log wage premium is incerasing for the more able, and this premium grew during the period 1984–1994 for individuals at all points in the ability distribution. The growth of this wage premium over time also appears to have followed a “smoother” linear path for high-ability individuals than individuals of lower ability.

This paper presents the development and piloted assessment of a full flight-envelope simulation model of a light business jet using a model stitching architecture. Individual state-space models and trim data for discrete flight conditions were combined to produce a continuous simulation model, which was integrated into a fixed-base simulation facility. Back-to-back flight/simulation piloted evaluations of a similar light business jet in flight and the stitched model in simulation were performed to assess the fidelity of the stitched model. Overall pilot impressions were that the stitched simulation model was representative of the actual aircraft. Simulation Fidelity Ratings were given to quantify simulation fidelity for each of the evaluated qualitative tasks, in which mostly Fidelity Level 1 ratings were assigned, suggesting full transfer of training for those tasks. Guidance on flight testing for the development of fixed-wing aircraft stitched models is provided.

This article reviews the Bayesian approach to estimation and inference. To begin with, it discusses two very popular and powerful algorithms for Bayesian model fitting – the Gibbs sampler and the Metropolis–Hastings algorithm – and offers a few observations regarding the role of the prior in both Bayesian and non-Bayesian research. It also illustrates the Gibbs algorithm in practice in two applications involving the effect of female obesity on log wages. Throughout these examples, focus is on strategies for diagnosing convergence of a posterior simulator and on exercises of posterior prediction.

The angiographic incidence of intramyocardial bridging (MB) is 0.7-4.5% [Angelini et al.: Prog Cardiovasc Dis 25:75-88, 1983]. Morphological and physiological patterns of MB have recently been described, observing coronary flow velocity patterns, intravascular ultrasound, and angiography [Flynn et al.: Cathet Cardiovasc Diagn 32:36-39, 1994; Ge et al.: Circ Res 89:1725-1732, 1994]. We describe a reversal of the normal flow velocity characteristics within a MB, due to a hemodynamically significant stenosis in the proximal left anterior descending artery (LAD). After successful percutaneous transluminal coronary angioplasty (PTCA) of the proximal LAD stenosis, there was normalization of the flow velocity pattern within the MB and the appearance of a spike and dome pattern distal to the MB.

A handling qualities experiment was run on the Vertical Motion Simulator using the GenHel math model configured for a UH60A Blackhawk helicopter. In order to obtain valid handling qualities ratings, the simulation system including the math model were optimized to provide realistic cues. The aircraft math model was adjusted to account for the simulator motion system delays and the motion systems gains and washouts were tuned for the bob-up, precision hover and sidestep tasks. The handling qualities ratings from this experiment showed good correlation to flight ratings.

A generic simulation model was developed for stability / control analysis and real-time simulation of ducted fan aircraft. The generic simulation model features a modified inflow model for ducted rotors, a basic model of control vane forces and moments, and empirical correction factors to account for duct thrust augmentation, duct pitching moment, and flow turning effects. Two empirical flow turning efficiency factors, one applied before the plane of the rotor and the other from freestream to far-wake flow, were investigated. A model of duct pitching moment was developed in which the duct thrust offset normalized by the rotor radius is given as a function of airspeed. Wind tunnel data and literature from several sources have been analyzed and compared in order to refine the pitching moment model and tune the empirical factors. Validation of the simulation model is provided through correlation studies with experimental data of a 29-inch ducted fan UAV. Steady-state and trim results obtained using the generic simulation model are presented and discussed.

We describe a new Bayesian estimation algorithm for fitting a binary treatment, ordered outcome selection model in a potential outcomes framework. We show how recent advances in simulation methods, namely data augmentation, the Gibbs sampler and the Metropolis-Hastings algorithm can be used to fit this model efficiently, and also introduce a reparameterization to help accelerate the convergence of our posterior simulator. Conventional “treatment effects” such as the Average Treatment Effect (ATE), the effect of treatment on the treated (TT) and the Local Average Treatment Effect (LATE) are adapted for this specific model, and Bayesian strategies for calculating these treatment effects are introduced. Finally, we review how one can potentially learn (or at least bound) the non-identified cross-regime correlation parameter and use this learning to calculate (or bound) parameters of interest beyond mean treatment effects.

The problem of mixing four-dimensional (4-D) equipped aircraft (aircraft equipped with onboard guidance systems that can predict and control the touchdown time of an aircraft to an accuracy of a few seconds throughout the descent) with unequipped aircraft in the terminal area has been investigated via a real-time air traffic control simulation study. The objective of this study was to develop scheduling algorithms and operational procedures for various traffic mixes that ranged from 25 to 15% 4-D equipped aircraft. Results indicate substantial reduction in controller workload and an increase in orderliness when more than 25% of the aircraft are 4-D equipped. Moreover, this is accomplished without increasing the workload or adding delays for the unequipped aircraft.

Fuel-conservative procedures have been investigated using real-time air traffic control simulations linked to two piloted simulators. The fuel-conservative procedures studied were profile descents and two types of landing approaches, delayed flap and IATA. The investigation determined the effect of these procedures on the ATC system operation. It examined the mixing of aircraft executing fuel-conservative approaches with those executing conventional approaches. The most difficult approach type mix of traffic was found to be 50% conventional and 50% delayed flap. However, for the test scenario chosen, arrival rates of at least 30 aircraft per hour were feasible and resulted in a net average fuel saving, even for the most difficult mix. Also, there is a fuel savings and reduced controller workload for the profile descent procedures.

Microcomputers could help reduce two of the principal fears of the elderly: inadequate income and loss of independence; yet there are indications that the elderly do not use computers very extensively because they see them as too complicated or because some of the physical impairments of advancing age make using standard systems too difficult for them. Previous research has shown a high degree of interest in computers among the aging, even in those over 85; however, the research has not focused on the elderly's special needs in the human-computer interface. Research is required on alternative input devices, such as the touchscreen and voice recognition, on menus and screen design, and on the use of color for coding or display background.

Although social behavior has been studied by sociologists, the absence of references to such work is strikingly apparent in many discussions of the behavioral aspects of obesity. This paper presents some sociologic notions and research that can contribute to the health care professional's understanding of the problems of obesity and its treatment possibilities. One such approach could well be the use of weight control programs predicated on rearranging the social environment in which obese people live and eat.

1 Alexander, B. (chairman), "Report of Department of Transportation Air Traffic Advisory Committee," Vols. 1 and 2, Dept. of Transportation, Washington, D.C., Dec. 1969. Blumstein, A., "The Landing Capacity of a Runway," Operations Research, Vol. 7, No. 6,1959, pp. 752-763. FAA, "The National Aviation System Plan, Ten Year Plan 1972-1981," (71-01686), March 1971, FAA, Washington, D.C. FAA, "The National Aviation System Policy Summary 1971," (7-10686), March 1971, FAA, Washington, D.C. Lister, S. F. and Raisbeck, G., "Approach to the Establishment of Practical Air Traffic Control Safety Goals," Contract No. FA70WA-2141, Little, Cambridge, Mass., May 1971. Raisbeck, G., Koopman, B. O., et al., "Air Traffic Control System Capacity," Contract No. DOT-FA70WA-2141, Little, Cambridge, Mass., Aug. 1970. Schriever, B. A. and Seifert, W. W., Air Transportation 1975 and Beyond: A Systems Approach, The MIT Press, Cambridge, Mass., 1968. Simpson, R., "Evaluation of Air Traffic Control Models and Simulations," Contract No. DOT-TSC-77, June 1971, MIT, Cambridge, Mass. Wilhelm, W. E., "Following Theory With Applications," Ph.D. dissertation, 1972, Virginia Polytechnic Inst. and State Univ., Blacksburg, Va.

Maximum clenching on an equilibrated occlusal splint yielded an increase of 17% in overall muscle activity over that of maximum intercuspation contributed mainly by masseter muscles. Maximum clenching on an anterior occlusal splint yielded a decrease of 13% in overall muscle activity compared with that of an equilibrated occlusal splint. When maximum clenching was performed with six left-sided teeth removed from contact while the left second molar remained in contact, there was no significant change in muscle activity when compared with that of an equilibrated occlusal splint. When left-sided muscles were compared with right-sided muscles for the same situation, there was no significant change. When maximum clenching was performed with all left-sided teeth removed from contact, there was a decrease of 21% in overall muscle activity compared with that of an equilibrated occlusal splint. When left-sided muscles were compared with right-sided muscles for the same situation, there was no significant change. Changes in the number of tooth contacts did not cause changes in the overall muscle activity during maximum clenching. Changes in the position of the tooth contacts altered the overall muscle activity during maximum clenching. Changes in occlusal contact symmetry did not cause changes in symmetry of muscle pairs during maximum clenching. Unilateral support produced the subjective response of pressure on the contralateral TMJ during maximum clenching.

In planning for a future air-traffic system that is to be extensively automated, it is necessary to confront the transition situation in which some percentage of the traffic must be handled by conventional means. A safe, efficient transition system is needed since initially not all aircraft will be able to respond to a more automated system, and since it is necessary to encourage users of the system to purchase the equipment required for the more automated operation. The specific problem addressed in this paper is that of time-scheduling a mix of 4D equipped aircraft (aircraft that can accurately meet a controllerspecified time-schedule at selected way points in the terminal area) when operating in conjunction with unequipped aircraft (aircraft that require air-traffic handling by means of standard vectoring techniques). First, a relationship between time-separation and system capacity is developed. The conditions under which a mix of traffic can lead to a capacity improvement have previously been derived. The time-separations are then incorporated into a set of scheduling algorithms which contain the required elements of flexibility needed for terminal-area operation, such as delaying aircraft and changing time-separations. The problem of reducing the size of time-separations allotted for vectored aircraft by means of computer assists to the controller is also addressed.

Two simulation experiments were conducted to investigate fuel-conservative approaches in an ATC environment. The first experiment centered on delayed flap and IATA approaches and how they could be mixed with conventional approaches under various traffic levels. The second experiment investigated the fuel savings potential of profile descents. The IATA approach appears to offer a good compromise between fuel efficiency and capacity in a mixed environment. While it saves about one half to two-thirds of the delayed flap approach fuel, it has less impact on capacity and controller workload in the 35 aircraft/hr traffic situation. The second experiment revealed that the profile descent procedures would result in at least a 10% average fuel savings during descent. In addition, since fewer radar vectors were required for profiles, the profiles showed a significant reduction in controller workload with respect to conventional aircraft.

An automation aid to assist air traffic controllers in efficiently spacing traffic and meeting arrival times at a fix has been developed at NASA Ames Research Center. The automation aid, referred to as the descent advisor (DA), is based on accurate models of aircraft performance and weather conditions. The DA generates suggested clearances, including both top-of-descent point and speed profile data, for one or more aircraft in order to achieve specific time or distance separation objectives. The DA algorithm is interfaced with a mouse-based, menu-driven controller display that allows the air traffic controller to interactively use its accurate predictive capability to resolve conflicts and issue advisories to arrival aircraft. This paper focuses on operational issues concerning the utilization of the DA, specifically, how the DA can be used for prediction, intrail spacing, and metering. In order to evaluate the DA, a real time simulation was conducted using both current and retired controller subjects. Controllers operated in teams of two, as they do in the present environment; issues of training and team interaction will be discussed. Evaluations by controllers indicated considerable enthusiasm for the DA aid, and provided specific recommendations for using the tool effectively.

The problem of mixing four-dimensional (4D) equipped aircraft (aircraft equipped with on-board guidance systems that can predict and control the touchdown-time of an aircraft to an accuracy of a few seconds throughout the descent) with unequipped aircraft in the terminal area has been investigated via a real-time air traffic control simulation study. The objective of this study was to develop scheduling algorithms and operational procedures for various traffic mixes that ranged from 25 percent to 75 percent 4D equipped aircraft. Results indicate substantial reduction in controller workload and an increase in orderliness when more than 25 percent of the aircraft are 4D equipped. Moreover, this is accomplished without increasing the workload or adding delays for the unequipped aircraft.

Air traffic management is considered as an AI problem, and planning concepts are developed for incorporation into an automation aid for enroute arrival controllers being developed by NASA. An Assumption-Based Truth Maintenance System is modified to include the nonmonotonicities inherent in the Air Traffic Control (ATC) domain, and it is noted under what circumstances the advantages of the ATMS in standard problem-solving domains carry over to planning. The noninteracting actions of the conceptualization are contrasted with the interacting actions of other domains. It is shown that the noninteracting nature of the ATC domain makes it possible to provide an efficient planner that avoids the frame problem.

The problem of mixing four-dimensional (4D) equipped aircraft - aircraft equipped with on-board guidance systems that can predict and control the touchdown time of an aircraft to an accuracy of a few seconds throughout the descent - with unequipped aircraft in the terminal area has been investigated via a real-time air traffic control simulation study. The objective of this study was to examine the effect of time errors (at 120 n. mi. from touchdown) on touchdown time scheduling, and to develop efficient algorithms and procedures to null the initial time errors prior to reaching the final control sector (30 n. mi. from touchdown). Results indicate that initial random errors of up to ±2 min can be handled via a single speed advisory issued in the arrival control sector, and thus the time schedule is not disrupted.

A prototype expert system has been developed for the time scheduling of aircraft into the terminal area. The three functions of the air-traffic-control schedule advisor are as follows: First, for each new arrival, it develops an admissible flight plan for that aircraft. Second, as the aircraft progresses through the terminal area, it monitors deviations from the aircraft's flight plan and provides advisories to return the aircraft to its assigned schedule. Third, if major disruptions such as missed approaches occur, it develops a revised plan. The advisor is operational on a Symbolics 3600, and is programmed in MRS (a logic programming language), Lisp, and Fortran.

A general scheduling algorithm for aircraft from terminal area entry to touchdown is developed. The method has the following novel features: (1) many speed classes of aircraft are considered and speed variations within classes and along portions of the flight path are permitted; (2) multiple paths are considered which may merge or diverge - the analysis is not restricted to a single runway nor to departures only; (3) landings are scheduled along conflict free flight paths in minimum time. The algorithm is currently being incorporated in a fast-time simulation of a STOL air traffic system.

1 Alexander, B. (chairman), "Report of Department of Transportation Air Traffic Advisory Committee," Vols. 1 and 2, Dept. of Transportation, Washington, D.C., Dec. 1969. Blumstein, A., "The Landing Capacity of a Runway," Operations Research, Vol. 7, No. 6,1959, pp. 752-763. FAA, "The National Aviation System Plan, Ten Year Plan 1972-1981," (71-01686), March 1971, FAA, Washington, D.C. FAA, "The National Aviation System Policy Summary 1971," (7-10686), March 1971, FAA, Washington, D.C. Lister, S. F. and Raisbeck, G., "Approach to the Establishment of Practical Air Traffic Control Safety Goals," Contract No. FA70WA-2141, Little, Cambridge, Mass., May 1971. Raisbeck, G., Koopman, B. O., et al., "Air Traffic Control System Capacity," Contract No. DOT-FA70WA-2141, Little, Cambridge, Mass., Aug. 1970. Schriever, B. A. and Seifert, W. W., Air Transportation 1975 and Beyond: A Systems Approach, The MIT Press, Cambridge, Mass., 1968. Simpson, R., "Evaluation of Air Traffic Control Models and Simulations," Contract No. DOT-TSC-77, June 1971, MIT, Cambridge, Mass. Wilhelm, W. E., "Following Theory With Applications," Ph.D. dissertation, 1972, Virginia Polytechnic Inst. and State Univ., Blacksburg, Va.

Fifty-two "hard core" mental patients who had been receiving psychotropic drugs were assigned to one of four subgroups, equated on descriptive variables, level of functioning, and bizarre behavior. All patients then participated in one of two social-environmental treatment programs, with one subgroup in each program receiving drug continuation in different capsule form, and the other receiving abrupt withdrawal with placebo substitution. Relative and interactional effects of drug conditions were evaluated 17 weeks after drug changes with concomitant exposure to active treatment programs, without patients, treatment staff, or assessors being aware that a drug study was underway. Except in early stages of treatment, where drugs interfered with improvement, continued low-dosage maintenance chemotherapy as prescribed in practice failed to produce direct effects or to contribute to responsiveness to the environmental programs.