OPTIMAL SEARCH ON SPATIAL PATHS WITH RECALL: THEORETICAL FOUNDATIONS

ABSTRACT This is the first of two articles which analyzes the problem of organizing an optimal sequential search among sites located in space. Here it is assumed that the payoffs or costs at sites are independent random variables with known distributions, and that recall of previously inspected sites is possible. Optimal sequential search is then taken to include optimization with respect to both stopping rules and search paths. In this article, it is shown that such optima always exist, and that under mild regularity conditions, optimal stopping rules on search paths always exhibit the classical reservation price property. In a companion article, a computational procedure for the optimization problem with continuous distributions is developed. It is illustrated for small examples, and optimal search paths are also computed for examples with discrete contributions.     

Planning under political transition—lessons from Cape Town's metropolitan planning forum

South Africa's recent process of transition, from an authoritarian to a liberal democratic political system, was accompanied by the use of innovative consensus‐seeking processes to develop new policy in a wide range of arenas. Given the spatial imprint of apartheid ideology on South African towns and cities, the development of new metropolitan plans was of central concern to those groupings with an interest in the future of the urban areas. A stakeholder forum process is evaluated which, between 1992 and 1994, produced a new spatial ‘vision’ for Cape Town, and both the factors which assisted consensus and those which appear to have limited the achievement of meaningful communication between forum participants are examined.     

Quantitative gated single photon emission computed tomography imaging: a counts-based method for display and measurement of regional and global ventricular systolic function

There is a considerable amount of data indicating that several major unfavorable cerebrovascular events are not randomly distributed over time, but show a peculiar distribution along the day, the week, and the months of the year. The authors review the available evidence on the chronobiological (circadian, weekly, and seasonal) patterns of onset of acute cerebrovascular diseases and variations in their possible triggering mechanisms. The existence of a peculiar chronobiological pattern in the onset of acute cerebrovascular disease, characterized by both circadian (morning and evening occurrence), circaseptan (last and first days of the week), and circannual (especially in winter) is confirmed, although differences depending on biological (gender, age), pathological (diabetes, hypertension, smoke, alcohol), cultural, social, and environmental factors exist. A deeper knowledge of the underlying pathophysiologic mechanisms could provide more effective insights for both preventive strategies and optimization of therapeutic approach.     

Tobacco, alcohol, and drug use in a primary care sample: 90-day prevalence and associated factors

The authors reviewed and presented the criteria used to classify the toxic effects of chemicals such as carcinogenic, irritation, corrosive, allergic, and fetotoxicity, as well as dermal absorption of chemical agents. The criteria for assigning symbols to the Polish list of chemical MAC values has not as yet been determined. Following the analysis it may be concluded that all chemical compounds, which satisfy the requirements should be indexed on the MAC list.     

Calbindin-D28k is regulated by adrenal steroids in hypothalamic tissue during prenatal development

We report the case of a 42 year-old woman with amyotrophic lateral sclerosis (ALS). Neurological examination showed spastic paraparesis and muscular atrophy of the upper extremities. Increased signal intensity areas were present in the lateral corticospinal tract of the brain and cervical spinal cord on a T2-weighted image. Decreased signal intensity of the motor cortex on the T2-weighted image appeared during the course of the illness. SPECT showed hypoperfusion confined to the motor cortex. The area of increased signal intensity in the cervical spinal cord on the T2-weighted MR images extended to the anterolateral columns of the spinal cord. The area of hypoperfusion in SPECT extended to the fronto-parietal area with the progression of the disease. These changes in the MRI and SPECT findings may reflect progressive degeneration of the upper motor neurons in ALS.     

Assessing enzyme substrate specificity using combinatorial libraries and electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry

A model experiment for the 'on-line' screening of substrate libraries by enzymes using combinatorial libraries in combination with electrospray ionization-Fourier transform ion cyclotron resonance (ESI-FTICR) mass spectrometry has been performed. The reaction between the electrophilic substrate 1-chloro-2,4-dinitrobenzene and component of a H-gamma-Glu-Cys-Xxx-OH library, catalyzed by glutathione-S-transferase, has been monitored. It shows the feasibility of 'two-dimensional' screening of substrate libraries by ESI-FTICR mass spectrometry.     

Effects of variation in system responsiveness on user performance in virtual environments

System responsiveness (SR) is defined as the elapsed time until a system responds to user control. SR fluctuates over time, so it must be described statistically with mean (MSR) and standard deviation (SDSR). In this paper, we examine SR in virtual environments (VEs), outlining its components and methods of experimental measurement and manipulation. Three studies of MSR and SDSR effects on performance of grasp and placement tasks are then presented. The studies used within-subjects designs with 11, 12, and 10 participants, respectively. Results showed that SDSR affected performance only if it was above 82 ms. Placement required more frequent visual feedback and was more sensitive to SR. We infer that VE designers need not tightly control SDSR and may wish to vary SR control based on required visual feedback frequency. These results may be used to improve the human-computer interface in a wide range of interactive graphical applications, including scientific visualization, training, mental health, and entertainment.     

Drug output from nebulizers is dependent on the method of measurement

The objective of this study was to determine whether current regulatory methods for assessing the output of nebulizers are appropriate for the delivery of nebulized steroid suspensions to patients. We studied a conventional jet nebulizer (the Intersurgical Cirrus), an open-vent nebulizer (the Medicaid Sidestream) and a breath-enhanced nebulizer (the Pari LC Plus), using a constant sampling flow or a sinusoidal pump to represent the breathing pattern of children from 6 months to adulthood. Recovery of budesonide released from the nebulizers onto filters was reduced when using breathing simulation compared with constant flow, and this reduction was greatest for the conventional nebulizer (Cirrus, 103 microg with constant flow to 4.4 microg with a 50 mL tidal volume; Pari, 176 microg to 25 microg). The open-vent nebulizer deposited very little budesonide on the filter at lower tidal volumes (4.5 microg with a 50 mL tidal volume), possibly because the enhanced flow of aerosol laden air was greater than the inspiratory flow from the breathing simulator. The output of the LC plus was reduced at high flow, from 176 microg at 20 L x min(-1) to 93 microg at 60 L x min(-1). Overall, the measured output varied by up to 700%, depending on the method used. These results suggest that breathing patterns dramatically alter the measured output of different nebulizers and that breathing simulation should be included as part of their assessment.