A 30-b integrated logarithmic number system processor

The authors describe an integrated processor that performs addition and subtraction of 30-b numbers in the logarithmic number system (LNS). This processor offers 5-MOPS performance in 3-μm CMOS technology, and is implemented in a two-chip set comprising 170 K transistors. Two techniques are used to achieve this precision in a moderate circuit area. Linear approximation of the LNS arithmetic functions using logarithmic arithmetic is shown to be simple due to the particular functions involved. A segmented approach to linear approximation minimizes the amount of table space required. Subsequent nonlinear compression of each lookup table leads to a further reduction in table size. The result is that a factor of 285 reduction in table size is achieved, compared to previous techniques. The circuit area of the implementation is minimized by optimizing the table parameters, using a computer program that accurately models ROM area. The implementation is highly pipelined, and produces one result per clock cycle using a ten-stage pipeline     

Stability of rack structures

Standard commercial pallet racking is used in warehouses, factories, shops and a multitude of other places where palletised goods are to be stored. The structural analysis of this type of structure is complicated by the semi-rigid nature of the beam-to-upright connection, which is different from one manufacturer to another.In the present paper an attempt has been made to provide a simple design approach to the stability of pallet rack structures, and the effect that the form of the moment-rotation characteristic has on the type of stability demonstrated by the system.Finally the role of small imperfections is studied, and the effect that they have on the maximum load carrying capacity of the structure is shown.     

Using fractal structure to describe nickel crystal morphology

The morphology of nickel crystals can be quantified using measurements of fractal structure. In the study described in this article, fractal dimensions of cross sections of 16 nickel samples were determined, and the numerical analysis indicates that the more rugged surfaces are characterized by higher fractal dimensions although the relationship between morphology and fractal dimension is relatively weak. However, the data also show that fractal dimension is a better predictor of morphology than apparent density, which is the measurement currently used. The nickel samples were also subjected to an avalanching disc technique that has the potential to separate out the differences in flow in the different types of nickel powder. The differences in flow between powders were ascribed to the similar gross morphologies of the particles, and the presence of shattered individual particles in the mix. For more information, contact A.E. Lewis, University of Cape Town, Precipitation and Crystallisation Research Facility, Department of Chemical Engineering, Rondebosch, 7701, South Africa; +27-21-650-4091; fax +27-21-689-7479; e-mail alison@chemeng.uct.ac.za.     

Solar building—European Union Research and Development Programmes

The European Commission's (EC) energy R&D programmes have completed two decades of progress. In the building sector special attention has been given to technology transfer and research dissemination, because of the particular problems which arise given the characteristics of the European construction industry, its diversity and fractured structure, and rather conservative nature.Projects such as the earlier Project MONITOR and BUILDING 2000, and the more recent INNOBUILD and SOLINFO projects and the Solar House programme together represent an unusual, if not unparalleled, effort aimed at bringing about technical change in building design and providing the necessary design and evaluation support and tools to professional architects and students and, to a lesser extent, to engineers. These projects are complemented by (and draw heavily from) an ambitious but clearly-targeted series of research projects investigating major energy-related issues concerning the heating, cooling and daylighting of buildings and deficiencies in knowledge of climate and human comfort, and building performance; activities such as the construction of passive solar test centres in ten EU Member States, each typically with four identical test cells equipped with interchangeable south walls, identical heating and cooling systems, sensors, and data acquisition systems. There is now in Europe considerable emphasis on the challenges of building in warmer climates, and on advancing daylighting design and performance and developing new materials.     

Effect of prenatal alcohol and cigarette exposure on two- and six-month-old infants'' adrenocortical reactivity to stress

Biologic data on benzene metabolite doses, cytotoxicity, and genotoxicity often show that these effects do not vary directly with cumulative benzene exposure (i.e., concentration times time, or c x t). To examine the effect of an alternate exposure metric, we analyzed cell-type specific leukemia mortality in Pliofilm workers. The work history of each Pliofilm worker was used to define each worker's maximally exposed job/department combination over time and the associated long-term average concentration associated with the maximally exposed job (LTA-MEJ). Using this measure, in conjunction with four job exposure estimates, we calculated SMRs for groups of workers with increasing LTA-MEJs. The analyses suggest that a critical concentration of benzene exposure must be reached in order for the risk of leukemia or, more specifically, AMML to be expressed. The minimum concentration is between 20 and 60 ppm depending on the exposure estimate and endpoint (all leukemias or AMMLs only). We believe these analyses are a useful adjunct to previous analyses of the Pliofilm data. They suggests that (a) AMML risk is shown only above a critical concentration of benzene exposure, measured as a long-term average and experienced for years, (b) the critical concentration is between 50 and 60 ppm when using a median exposure estimate derived from three previous exposure assessments, and is between 20 and 25 ppm using the lowest exposure estimates, and (c) risks for total leukemia are driven by risks for AMML, suggesting that AMML is the cell type related to benzene exposure.     

Activated partial thromboplastin time and outcome after thrombolytic therapy for acute myocardial infarction: results from the GUSTO-I trial

BACKGROUND: Although intravenous heparin is commonly used after thrombolytic therapy, few reports have addressed the relationship between the degree of anticoagulation and clinical outcomes. We examined the activated partial thromboplastin time (aPTT) in 29,656 patients in the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries (GUSTO-I) trial and analyzed the relationship between the aPTT and both baseline patient characteristics and clinical outcomes. METHODS AND RESULTS: Intravenous heparin was administered as a 5000-U bolus followed by an initial infusion of 1000 U/h, with dose adjustment to achieve a target aPTT of 60 to 85 seconds. aPTTs were collected 6, 12, and 24 hours after thrombolytic administration. Higher aPTT at 24 hours was strongly related to lower patient weight (P < .00001) as well as older age, female sex, and lack of cigarette smoking (all PT< .0001). At 12 hours, the aPTT associated with the lowest 30-day mortality, stroke, and bleeding rates was 50 to 70 seconds. There was an unexpected direct relationship between the aPTT and the risk of subsequent reinfarction. There was a clustering of reinfarction in the first 10 hours after discontinuation of intravenous heparin. CONCLUSIONS: Although the relationship between aPTT and clinical outcome was confounded to some degree by the influence of baseline prognostic characteristics, aPTTs higher than 70 seconds were found to be associated with higher likelihood of mortality, stroke, bleeding, and reinfarction. These findings suggest that until proven otherwise, we should consider the aPTT range of 50 to 70 seconds as optimal with intravenous heparin after thrombolytic therapy.     

Rheological Property and Stress Development during Drying of Tape-Cast Ceramic Layers

Rheological property and stress development of tape-cast ceramic layers derived from nonaqueous alumina (A1₂O₃)-poly(vinyl butyral) (PVB) suspensions were observed during drying. Casting suspensions exhibited strong shear-thinning behavior, with a low shear Newtonian plateau apparent viscosity >10² Pa^.s. The apparent suspension viscosity displayed a power-law dependence on the A1₂O₃ volume fraction during the initial stage of drying (<30% solvent loss). Stress development, measured by a cantilever deflection method, and parallel weight loss measurements were performed during the drying of tape-cast layers and pure binder coatings. Maximum drying stresses (σ_max) of 1.37-0.77 MPa were observed for plasticized tapes cast at gap heights of 150-400 μm. In contrast, nonplasticized tapes of similar thickness displayed a more gradual stress increase, with σ_max values approximately an order of magnitude higher than their plasticized counterparts. The stress histories of the corresponding binder coatings were quite similar to the tape-cast layers, albeit slightly lower σ _max values were observed. Stresses decayed beyond σ_max with a logarithmic time dependence to an almost constant value of 0.2-0.4 MPa for the plasticized tapes. Based on these observations, process methodologies have been offered to minimize stress development and retention in tape-cast ceramic layers     

Intermodality, retrospective image registration in the thorax

The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.