Intra-event variability of Escherichia coli and total suspended solids in urban stormwater runoff

Sediment levels are important for environmental health risk assessments of surface water bodies, while faecal pollution can introduce significant public health risks for users of these systems. Urban stormwater is one of the largest sources of contaminants to surface waters, yet the fate and transport of these contaminants (especially those microbiological) have received little attention in the literature. Stormwater runoff from five urbanized catchments were monitored for pathogen indicator bacteria and total suspended solids in two developed countries. Multiple discrete samples were collected during each storm event, allowing an analysis of intra-event characteristics such as initial concentration, peak concentration, maximum rate of change, and relative confidence interval. The data suggest that a catchment’s area influences pollutant characteristics, as larger catchments have more complex stormwater infrastructure and more variable pollutant sources. The variability of total suspended solids for many characteristics was similar to Escherichia coli, indicating that the variability of E. coli may not be substantially higher than that of other pollutants as initially speculated. Further, variations in E. coli appeared to be more commonly correlated to antecedent climate, while total suspended solids were more highly correlated to rainfall/runoff characteristics. This emphasizes the importance of climate on microbial persistence and die off in urban systems. Discrete intra-event concentrations of total suspended solids and, to a lesser extent E. coli, were correlated to flow, velocity, and rainfall intensity (adjusted by time of concentrations). Concentration changes were found to be best described by adjusted rainfall intensity, as shown by other researchers. This study has resulted in an increased understanding of the magnitude of intra-event variations of total suspended solids and E. coli and what physical and climatic parameters influence these variations.     

Non‐Volatile Organic Memory Elements Based on Carbon‐Nanotube‐Enabled Vertical Field‐Effect Transistors

High‐performance non‐volatile memory elements based on carbon‐nanotube‐enabled vertical field‐effect transistors (CN‐VFETs) are demonstrated. A thin crosslinking polymer layer, benzocyclobutene (BCB), on top of the gate dielectric acts as the charge storage layer. This results in a large, fully gate sweep programmable, hysteresis in the cyclic transfer curves exhibiting on/off ratios >4 orders of magnitude. The carbon nanotube random network source electrode facilitates charge injection into the charge storage layer, realizing the strong memory effect without sacrificing mobility in the vertical channel. Given their intrinsically simple fabrication and compact size CN‐VFETs could provide a path to cost‐effective, high‐density organic memory devices.     

Novel Approach to Improve Electronics Reliability in the Next Generation of US Army Small Unmanned Ground Vehicles Under Complex Vibration Conditions

The functionality of next generation the US Army’s platforms, such as the Small Unmanned Ground Vehicles and Small Unmanned Arial Vehicles, is strongly dependent on the reliability of electronics-rich devices. Thus, the performance and accuracy of these systems will be dependent on the life-cycle of electronics. These electronic systems and the critical components in them experience extremely harsh environments such as shock and vibration. Therefore, it is imperative to identify the failure mechanisms of these components through experimental and virtual failure assessment. One of the key challenges in re-creating life-cycle vibration conditions during design and qualification testing in the lab is the re-creation of simultaneous multiaxial excitation that the product experiences in the field. Instead, the common practice is to use sequential single-axis excitation in different axes or uncontrolled multiaxial vibration on repetitive shock shakers. Consequently, the dominant failure modes in the field are sometimes very difficult to duplicate in a laboratory test. This paper presents the joint effort by the US Army Materiel Systems Analysis Activity (AMSAA) and the Center of Advanced Life Cycle Engineering (CALCE) at the University of Maryland to develop test methods and analytical models that better capture unforeseen design weaknesses prior to the qualification phase, by better replication of the life-cycle vibration conditions. One approach was to utilize a novel multi-degrees-of-freedom (M-DoF) electrodynamic shaker to ruggedize designs for fatigue damage due to multi-directional random vibration. The merits of vibration testing methods with six-DoF shaker and cost saving associated with such an approach will be addressed in this paper. There is a potential for M-DoF to detect critical design vulnerabilities earlier in the development cycle than has been traditionally possible with existing shaker technologies; and therefore to produce more cost effective, reliable and safe systems for the warfighters.     

Classroom conditions and CO2 concentrations and teacher health symptom reporting in 10 New York State Schools

This study assessed the relationship between teacher‐reported symptoms and classroom carbon dioxide (CO₂) concentrations. Previous studies have suggested that poor indoor ventilation can result in higher levels of indoor pollutants, which may affect student and teacher health. Ten schools (9 elementary, 1 combined middle/high school) in eight New York State school districts were visited over a 4‐month period in 2010. Carbon dioxide concentrations were measured in classrooms over 48‐h, and teachers completed surveys assessing demographic information and self‐reported symptoms experienced during the current school year. Data from 64 classrooms (ranging from 1 to 9 per school) were linked with 68 teacher surveys (for four classrooms, two surveys were returned). Overall, approximately 20% of the measured classroom CO₂ concentrations were above 1000 parts per million (ppm), ranging from 352 to 1591 ppm. In multivariate analyses, the odds of reporting neuro‐physiologic (i.e., headache, fatigue, difficulty concentrating) symptoms among teachers significantly increased (OR = 1.30, 95% CI = 1.02–1.64) for every 100 ppm increase in maximum classroom CO₂ concentrations and were non‐significantly increased in classrooms with above‐median proportions of CO₂ concentrations greater than 1000 ppm (OR = 2.26, 95% CI = 0.72–7.12).     

Identifying the role of fly ash properties for minimizing sulfate-heave in lime-stabilized soils

The paper describes a study carried out to examine the effects of fly ash in limiting damaging sulfate-heave (swelling) in lime-stabilized soils. This considered three clays with various sulfate levels; seven fly ashes covering a range of physical and chemical properties, and stored under different conditions (dry, stockpiled and ponded); and a typical quicklime. The initial part of the study examined the effects of fly ash (applied at levels of 6 to 24% by mass of dry soil) on compaction (in terms of density/moisture relationships) of the lime-stabilized soils (using 3.0% lime) to establish mix compositions and provide an insight to their resulting structure. This indicated that maximum dry density (MDD) and optimum moisture content (OMC) were influenced by the characteristics of fly ash (reducing and increasing respectively with increasing fly ash coarseness and loss-on-ignition (LoI; including that under wet storage)) and, depending on these, by the level of application. Tests for sulfate-heave were made following the BS EN 13286-49 volumetric swelling method. Fly ash gave systematic reductions in sulfate-heave with increasing application level up to 24% for the lime-stabilized soils tested. It was found that coarse, high LoI fly ashes, stored under wet conditions, were most effective in limiting the process, suggesting that the coarser structure obtained during compaction with these materials, i.e. lower MDD, is an important factor influencing this. The presence of high sulfate levels in fly ash reduced the effectiveness of the material in this role. The practical implications are considered and a nomogram relating fly ash fineness and application level, MDD and sulfate-swelling is developed, which demonstrates a possible methodology for material selection with regard to minimizing damage.     

Contours and borders in animated mimic displays

Previous research has indicated that ambiguities in apparent motion (e.g., direction, rate) can result when color table techniques are used to produce animation in mimic displays. Two experiments were conducted to investigate alternative display designs in which contours (angled vs. straight) and borders (explicit vs. implicit) were varied. In Experiment 1, contours, borders, and temporal frequency interacted. At 5 Hz angled contours improved accuracy significantly. At 10 Hz explicit borders improved accuracy significantly with angled contours but degraded accuracy significantly with straight contours. In Experiment 2, the design of the angled contours was changed to convey less information and an additional border condition was added. Once again, borders and contours interacted: The widest explicit border degraded accuracy with straight contours. Angled contours also improved latency performance. The results suggest that angled contours can reduce ambiguity and improve the effectiveness of animated mimic displays by providing a redundant encoding of rate information. However, this benefit must be weighed against the associated computational costs. A secondary finding was that when contours are straight the borders should be implicit, not explicit. Alternative design solutions for animated mimic displays are also discussed.