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International air travel is now widely recognised as one of the primary mechanisms responsible for the transnational movement and global spread of SARS-CoV-2. Monitoring the viral load and novel lineages within human-derived wastewater collected from aircraft and at air transport hubs has been proposed as an effective way to monitor the importation frequency of viral pathogens. The success of this approach, however, is highly dependent on the bathroom and defecation habits of air passengers during their journey. In this study of UK adults (n = 2103), we quantified the likelihood of defecation prior to departure, on the aircraft and upon arrival on both short- and long-haul flights. The results were then used to assess the likelihood of capturing the signal from infected individuals at UK travel hubs. To obtain a representative cross-section of the population, the survey was stratified by geographical region, gender, age, parenting status, and social class. We found that an individual's likelihood to defecate on short-haul flights (< 6 h in duration) was low (< 13 % of the total), but was higher on long-haul flights (< 36 %; > 6 h in duration). This behaviour pattern was higher among males and younger age groups. The maximum likelihood of defecation was prior to departure (< 39 %). Based on known SARS-CoV-2 faecal shedding rates (30–60 %) and an equal probability of infected individuals being on short- (71 % of inbound flights) and long-haul flights (29 %), we estimate that aircraft wastewater is likely to capture ca. 8–14 % of SARS-CoV-2 cases entering the UK. Monte Carlo simulations predicted that SARS-CoV-2 would be present in wastewater on 14 % of short-haul flights and 62 % of long-haul flights under current pandemic conditions. We conclude that aircraft wastewater alone is insufficient to effectively monitor all the transboundary entries of faecal-borne pathogens but can form part of a wider strategy for public heath surveillance at national borders.

A wide variety of semiconductor devices utilizing gallium arsenide are currently under development by the military for use in secure communication, improved surveillance, and high speed digital logic systems. The GaAs field effect transistor, a critical component in these systems, is experiencing a rapidly expanding use in oscillator, mixer, logic element, power amplification, and low-noise/high-gain applications. However, the full potential of this device has not been realized, partly because of poor and unpredictable quality semi-insulating GaAs substrates. More specifically, native defects, electrically active impurities, and diffusing charge traps are problems associated with commercial substrates. A silicon- and carbon-free modification of the liquid encapsulated Czochralski technique is described which yields high purity semi-insulating GaAs (approximately 10 to the 8th ohm-cm) without the intentional addition of charge compensators. The technique employs liquid encapsulated compounding of GaAs at nitrogen pressures to 100 atm, ultrapure elements, and pyrolytic boron nitride crucibles. A high pressure (135 atm) Varian HPCZ Czochralski crystal puller is employed for both compounding and crystal growth. (Author)

The requirement for low-threshold high-efficiency laser sources for miniaturized rangefinder and fiber optic communication applications has led to the study of rare earth pentaphosphate compounds. Neodymium pentaphosphate (NdPP) has recently emerged as a promising 1.05 micrometer laser material operating in pulsed and cw modes, with thresholds of the latter reported less than 1 milliwatt. In contrast to doped lasers such as Nd:YAG, NdPP is a stoichiometric compound (NdP5O14) which accommodates up to thirty times more Nd than YAG. The evaluation and testing of NdPP lasers in prototype components using transverse and longitudinal optical pumping has been hindered due to the limited size (several mm), availabilty, and quality of the single crystals. We have devised unique modifications of conventional solution growth techniques in order to control reaction kinetics and precipitation rates. The largest bulk single crystals (greater than 1 cm) of yttrium and lanthanum substituted NdPP presently available were grown by these modified techniques. We have observed laser action in as-grown 90% Nd 10% Y pentaphosphate crystals with dimensions typically 4.5x3 mm in diamond-shaped cross section by 2 mm thick.

DTFH61-93-C-00133, This interim report documents the field performance of nine concrete pavement projects that incorporate recycled concrete aggregate (RCA) in the construction of the pavement. Multiple sections were evaluated on many of the nine projects, due to perceived differences in performance levels or variations in pavement design (such as the use of virgin aggregate or the inclusion of dowel bars). All told, a total of 17 sections (of which 12 contain RCA) were subjected to an extensive field testing program, consisting of pavement condition surveys, drainage surveys, falling weight deflectometer (FWD) testing, coring, and serviceability assessments. A minimum of eight cores were retrieved from each section for laboratory evaluation of compressive strength, split tensile strength, dynamic elastic modulus, static elastic modulus, and thermal coefficient of expansion, as well as for volumetric surface testing and petrographic analyses. Each of the 17 sections included in the investigation is described in detail. Performance observations and results from the FWD and laboratory testing are presented, with emphasis on evaluating the effect of RCA on pavement performance. An overall summary is provided that synthesizes the findings and conclusions of the field testing program. A laboratory-based research effort is currently being planned to provide additional insight on the behavior of concrete mixtures using RCA. Those laboratory-based results, taken in conjunction with the results of the field testing program, will be used to produce guidelines for the design of recycled concrete mixtures and to develop recommendations for the design of concrete pavements using RCA.

DTFH61-96-C-00073, The performance of concrete pavements can be adversely affected by the concrete's inability to resist the environment in which it is placed. This lack of durability can occur even when the structural design of the pavement is adequate. The distresses that result from this lack of durability are referred to herein as materials-related distress (MRD). This report documents the investigation of MRD in concrete pavements and the development of a set of systematic guidelines for the evaluation of MRD. The guidelines developed cover three major areas of MRD: field distress surveys, pavement sampling, and sample handling; laboratory testing, data analysis, and interpretation; and treatment, rehabilitation, and prevention.