Role of Additive Adsorption in the Mitigation of Wear

The mathematical model of adhesive wear and its control by surface adsorption of a single-component lubricant has been expanded to include an additive as a second component. The model has been tested with experimental wear rate results as a function if additive concentration for both liquid and vapor phase lubricants. A satisfactory fit of the data to the model is observed, and the calculated values for the equilibrium constant and the heat of adsorption for long-chain polar compounds from cetane solution on steel surfaces are amine > acid > alcohol, the same trend as observed in adsorption studies. The ratio of the effective molecular size of the adsorbed molecules can be calculated and used as a parameter in testing the model, or for gaining understanding about the nature of the active antiwear specie.     

Analysis of a complete DNA–protein affinity landscape

Properties of biological fitness landscapes are of interest to a wide sector of the life sciences, from ecology to genetics to synthetic biology. For biomolecular fitness landscapes, the information we currently possess comes primarily from two sources: sparse samples obtained from directed evolution experiments; and more fine-grained but less authentic information from ‘in silico’ models (such as NK-landscapes). Here we present the entire protein-binding profile of all variants of a nucleic acid oligomer 10 bases in length, which we have obtained experimentally by a series of highly parallel on-chip assays. The resulting complete landscape of sequence-binding pairs, comprising more than one million binding measurements in duplicate, has been analysed statistically using a number of metrics commonly applied to synthetic landscapes. These metrics show that the landscape is rugged, with many local optima, and that this arises from a combination of experimental variation and the natural structural properties of the oligonucleotides.     

Ageing of HDPE geomembrane exposed to air,water and leachate at different temperatures

The latest findings regarding the long-term performance and service life of HDPE geomembrane (GM) samples exposed to air, water and leachate are presented based on data from samples that have been ageing for 8–10 years. Some of the GM samples are in Stage II, some in Stage III and some have completed all three stages of the service life. The paper provides: (1) improved data on antioxidant depletion rates for GMs immersed in air, water and leachate; (2) estimates of antioxidant depletion time (Stage I) at typical liner temperatures in air, water and leachate and, based on this data, an estimate for a composite liner at typical liner temperatures; (3) data regarding the changes in the physical and mechanical properties of the GM samples with time; (4) a surface analysis of virgin and aged GMs; (5) an initial estimate of the induction time (Stage II) and polymer degradation time (Stage III) and service lives of GM in laboratory immersion tests; and (6) predictions of the service life of leachate immersed GM at typical landfill temperatures. Based on these predictions, it appears likely that the service life of the specific GM tested immersed in leachate is likely to exceed 700 years and will probably be of the order of 1000 years (or longer) at 20 °C, more than 150 years and likely 225–375 years at 35 °C and more than 40 years and likely 50–90 years at 50 °C. The service life in a liner configuration may be expected to be longer than predicted here for immersion in leachate.     

Diffusive Transport of VOCs through LLDPE and Two Coextruded Geomembranes

The diffusive properties of two coextruded geomembranes, one with a polyamide inner core and the other with an ethylene vinyl-alcohol (EVOH) inner core, and a standard 0.53-mm (20-mil) linear low-density polyethylene (LLDPE) geomembrane were examined. Diffusion and sorption laboratory tests were performed to estimate the parameters controlling diffusive migration, including the partitioning, diffusion, and permeation coefficients of the geomembrane in both the aqueous and vapor phases. Results indicate a significant reduction in mass flux through the coextruded geomembranes compared to conventional LLDPE. The EVOH coextruded geomembrane had the lowest permeation coefficients (Pg) with a range of (2–6)×10?12?m2?s?1 for diffusion from the aqueous phase. These values for EVOH are upper bounds and the actual values may be lower than as stated. The polyamide (nylon) coextruded geomembrane had higher values than for EVOH, with a Pg range of (0.7–2.2)×10?11?m2?s?1 from the aqueous phase. The highest permeation coefficients were for the standard 20-mil LLDPE, which ranged from (0.6–1.1)×10?10?m2?s?1. Thus the permeation coefficient for LLDPE was about one order of magnitude greater than for the nylon coextruded and at least two orders of magnitudes higher than for the EVOH coextruded geomembrane. Both coextruded geomembranes showed decreased Pg values and therefore improved diffusive resistance to volatile organic compounds over traditional 0.56-mm PVC geomembranes. The EVOH geomembrane showed a 5–12-fold decrease in Pg in comparison to a 2.0-mm high density polyethylene geomembrane.     

Air exchange rates and migration of VOCs in basements and residences

Basements can influence indoor air quality by affecting air exchange rates (AERs) and by the presence of emission sources of volatile organic compounds (VOCs) and other pollutants. We characterized VOC levels, AERs, and interzonal flows between basements and occupied spaces in 74 residences in Detroit, Michigan. Flows were measured using a steady‐state multitracer system, and 7‐day VOC measurements were collected using passive samplers in both living areas and basements. A walk‐through survey/inspection was conducted in each residence. AERs in residences and basements averaged 0.51 and 1.52/h, respectively, and had strong and opposite seasonal trends, for example, AERs were highest in residences during the summer, and highest in basements during the winter. Airflows from basements to occupied spaces also varied seasonally. VOC concentration distributions were right‐skewed, for example, 90th percentile benzene, toluene, naphthalene, and limonene concentrations were 4.0, 19.1, 20.3, and 51.0 μg/m³, respectively; maximum concentrations were 54, 888, 1117, and 134 μg/m³. Identified VOC sources in basements included solvents, household cleaners, air fresheners, smoking, and gasoline‐powered equipment. The number and type of potential VOC sources found in basements are significant and problematic, and may warrant advisories regarding the storage and use of potentially strong VOCs sources in basements.     

Nine-analyte detection using an array-based biosensor

A fluorescence-based multianalyte immunosensor has been developed for simultaneous analysis of multiple samples. While the standard 6 x 6 format of the array sensor has been used to analyze six samples for six different analytes, this same format has the potential to allow a single sample to be tested for 36 different agents. The method described herein demonstrates proof of principle that the number of analytes detectable using a single array can be increased simply by using complementary mixtures of capture and tracer antibodies. Mixtures were optimized to allow detection of closely related analytes without significant cross-reactivity. Following this facile modification of patterning and assay procedures, the following nine targets could be detected in a single 3 x 3 array: Staphylococcal enterotoxin B, ricin, cholera toxin, Bacillus anthracis Sterne, Bacillus globigii, Francisella tularensis LVS, Yersiniapestis F1 antigen, MS2 coliphage, and Salmonella typhimurium. This work maximizes the efficiency and utility of the described array technology, increasing only reagent usage and cost; production and fabrication costs are not affected.     

Interpreting computer code in a computer‐based learning system for novice programmers

Although the principles of writing compilers and interpreters are well known, we have found that the ideas needed to develop an interpreter for the express purpose of allowing direct interaction with the running code do not yet appear to have been published in an academic context. We describe a programming method that can be used for the production of an interpreter for common object‐oriented languages such as C++, Java and C#. The main purpose of the interpreter is to parse short, relatively simple programs and allow direct interaction between the user and the running code. Such a system is useful for projects such as OGRE, which is an educational tool allowing students to visualize in three‐dimensional graphics the state of a program as it runs. The interpreter works by first parsing the source code and building up a data structure capable of representing the program's source code in a form that can be used to both run the program and extract detailed information from the running program. This extraction allows for novel uses of the interpreter, such as forming the basis for a visualization system that must display and provide such information to the user as they watch their executing program. This paper considers the construction of such an interpreter specifically for C++, but the principles should be the same for other similar languages such as Java and C#. We cover the main tasks required of the programmer to create and use the data structure, highlighting areas such as its design, initial construction during parsing, and techniques required to use it for interpretation. These include the ability for the data structure to intelligently clone subsets of itself when multiple copies of one of its elements are required by the running program, how it handles C++'s complicated function overloading and overriding rules, and how inheritance and polymorphism can be supported. Copyright © 2005 John Wiley & Sons, Ltd.     

Local haemodynamics of arterial bypass graft anastomoses

One of the main causes of failure of expanded polytetrafluoroethylene (PTFE) bypass grafts used in the lower limbs is the development of myointimal hyperplasia (MIH). Clinical studies show that higher patency rates can be obtained with the use of an autologous vein cuff (the Miller cuff) interposed between the graft and artery. The reasons for the improved performance are still unclear, but preliminary studies suggest that the change in local haemodynamics due to the cuff geometry may be the significant factor rather than the presence of autologous material. If this is the case, then PTFE grafts can be produced with an integral cuff, i.e. a precuffed graft, with similar haemodynamic patterns to that of the Miller cuff. In this paper, two different types of precuffed graft are presented and their flow patterns are compared with those recorded in the Miller cuff and the conventional end-to-side anastomosis. The haemodynamic studies were carried out using optically clear silicone rubber models under simulated in vivo pulsatile flow conditions. Flow structures similar to those observed in the Miller cuff were seen in the precuffed grafts.     

Design and operation of a very large ring laser gyroscope

The design and initial operation of a vertical square He-Ne ring laser G0 with a perimeter of 14 m is discussed. This builds on earlier demonstrations of the feasibility of large ring lasers (perimeter approximately 4 m) for single-mode gyroscope operation and with lesser pulling than navigation gyroscopes. With servoing of the rf excitation to yield single-mode operation, G0 gave a quality factor 1 x 10(12) and a Sagnac line with a frequency of 287.8 +/- 1.0 Hz induced by Earth rotation Omega(E). This has confirmed some vital questions over the feasibility of very large gyroscopes for geodetic measurements at the level of 10(-9) Omega(E).