Interpreting aggregate wage growth

This paper analyzes the relationship between aggregate wages and individual wages when there is time series variation in employment and in the dispersion of wages. A new and easily implementable framework for the empirical analysis of aggregation biases is developed. Aggregate real wages are shown to contain three important bias terms: one associated with the dispersion of individual wages, a second reflecting the distribution of working hours, and a third deriving from compositional changes in the (selected) sample of workers. Noting the importance of these issues for recent experience in Britain, data on real wages and participation for British male workers over the period 1978-1996 are studied. A close correspondence between the estimated biases and the patterns of differences shown by aggregate wages is established. This is shown to have important implications for the interpretation of real wage growth over this period

Standard environmental testing practices

Manual on procedural requirements for performing certain environmental tests on space flight equipment provides information for test equipment designers, quality control and production engineers. Contents of manual are summarized

We Should Search for Life in Mars N. Polar Ground Ice

The 2008 Phoenix Mars lander mission sampled ground ice at 68N latitude. Mission results, considered along with climate modeling studies, suggest that the site is habitable for life during high obliquity periods. The Icebreaker mission has been proposed to the NASA Discovery program to search for biosignatures produced during habitable periods. This paper explores its rationale and approach

Assessing Habitability: Lessons from the Phoenix Mission

The Phoenix mission's key objective was to search for a habitable zone. The Phoenix lander carried a robotic arm with digging scoop to collect soil and icy material for analysis with an instrument payload that included volatile mineral and organic analysis(3) and soil ionic chemistry analysis (4). Results from Phoenix along with theoretical modeling and other previous mission results were used to evaluate the habitability of the landing site by considering four factors that characterize the environments ability to support life as we know it: the presence of liquid water, the presence of an energy source to support metabolism, the presence of nutrients containing the fundamental building blocks of life, and the absence of environmental conditions that are toxic to or preclude life. Phoenix observational evidence for the presence of liquid water (past or present) includes clean segregated ice, chemical etching of soil grains, calcite minerals in the soil and variable concentrations of soluble salts5. The maximum surface temperature measured was 260K so unfrozen water can form only in adsorbed films or saline brines but warmer climates occur cyclically on geologically short time scales due to variations in orbital parameters. During high obliquity periods, temperatures allowing metabolism extend nearly a meter into the subsurface. Phoenix discovered ~1%w/w perchlorate salt in the soil, a chemical energy source utilized by a wide range of microbes. Nutrient sources including C, H, N, O, P and S compounds are supplied by known atmospheric sources or global dust. Environmental conditions are within growth tolerance for terrestrial microbes. Summer daytime temperatures are sufficient for metabolic activity, the pH is 7.8 and is well buffered and the projected water activity of a wet soil will allow growth. In summary, martian permafrost in the north polar region is a viable location for modern life. Stoker et al. presented a formalism for comparing the habitability of various regions visited to date on Mars that involved computing a habitability probability, defined as the product of probabilities for the presence of liquid water (P(sub lw)), energy (P(sub e)), nutrients (P(sub ch)), and a benign environment (P(sub b)). Using this formalism, they argued that the Phoenix site was the most habitable of any site visited to date by landed missions and warranted a follow up mission to search for modern evidence of life. This paper will review that conclusion in view of more recent information from the Mars Exploration Rovers and Mars Science Lander missions

The Goals and Approach of the Phoenix Mission for Evaluating the Habitabiity of the Northern Plains on Mars

The first goal of the Mars Exploration program, as defined by the Mars Exploration Payload Analysis Group (MEPAG) is to determine if life ever arose on Mars [1]. The Phoenix landing site was chosen to sample near surface ground ice in the Northern Plains discovered by the GRS experiment on Mars Odyssey [2]. A goal of Phoenix is to determine whether this environment was habitable for life at some time in its history

Low Cost Mars Sample Return Utilizing Dragon Lander Project

We studied a Mars sample return (MSR) mission that lands a SpaceX Dragon Capsule on Mars carrying sample collection hardware (an arm, drill, or small rover) and a spacecraft stack consisting of a Mars Ascent Vehicle (MAV) and Earth Return Vehicle (ERV) that collectively carry the sample container from Mars back to Earth orbit

Investigation of the origin of shallow gas in outer Moray Firth open blocks 15/20c and 15/25d

This report briefly describes the evidence for the origin of shallow gas in Outer Moray Firth open blocks 15/20c and 15/25d. Sea floor pockmarks are known to occur within these blocks, and they indicate the seepage of gas from shallow levels into the local water column. An environmental concern is that any industry activity in these blocks must not plumb into any component of the system that is sustaining the gas seepages at sea bed. The conclusions of this study are: 1. Interpretation of the available BGS shallow seismic data and commercial site investigation data shows that gas is seeping from sea bed in three large active pockmark complexes in approximately 150 m or more water depth: the Challenger Pockmark Complex in the north of block 15/25d, the Scanner Pockmark Complex in the south of block 15/25d and the Scotia Pockmark which is adjacent to the north-east of the Scanner Pockmark Complex. 2. A review of the peer-reviewed scientific publications indicates that the majority of the arguments based on isotope analyses of gas and authigenic carbonate are for a predominantly biological origin for the gas seeping from the active pockmarks. However, biogenic isotopic signatures in the Gulf of Mexico and the North Sea are thought to have been generated when thermogenic hydrocarbons in shallow sediments were re-cycled by bacteria to produce ‘secondary’ methane with an identical isotopic signature to biogenic methane. Thus, the isotopic data derived from the Scanner Pockmark Complex do not provide a secure basis for determining whether the gas escaping from the pockmarks in block 15/25 is primarily biogenic or thermogenic in origin. 3. Interpretations completed during this project indicate that gas seeping to sea bed in the largest pockmarks is reservoired within the uppermost part of the Aberdeen Ground Formation, where it is preserved between buried sub-glacial channels. The gas seepages at sea bed are fed from an almost continuous blanket of buried gas-charged sediments situated between the sub-glacial channel margins at approximately 280-300 ms two-way time (around 120 m below sea bed) in the northern part of block 15/25d. 4. An empirical conclusion from distribution patterns observed in the interval between sea bed and 400 ms two-way time is that loss of shallow gas from the gas-charged interval at approximately 280-300ms two-way time will cut off the supply of shallow gas to the active pockmarks. Dry well 15/25b-1A, located immediately to the north of the Scanner Pockmark Complex, appears to have been drilled on the margin of the shallow gas reservoir. A recommendation is that future development operations should not disturb the shallow gas reservoir. 5. All of the hydrocarbon discoveries made within and around the study area are oil. The nearest Upper Jurassic Kimmeridge Clay Formation principal thermogenic gas kitchen lies some 30 km to the south-east, in the Fisher Bank Basin. Gas has been proved to have migrated up into Mid-Eocene sandstones (e.g. Alba Field) in that basin. Although it is possible that further vertical migration might have been achieved through minor faults and fractures in the Late Eocene to Pliocene, no evidence was observed in the 3D data to connect the location of the active pockmarks with supply from the thermogenic gas kitchen. For example, no gas chimneys have been observed within the Tertiary section on 3D seismic data across the study area.. Although no major faults have been found in 3D seismic data that transect the entire Eocene to Pliocene interval, minor polygonal faulting has been observed within the upper part of the Hordaland Group

Telepresence in the human exploration of Mars: Field studies in analog environments

This paper describes the role of telepresence in performing exploration of Mars. As part of an effort to develop telepresence to support Mars exploration, NASA is developing telepresence technology and using it to perform exploration in space analog environments. This paper describes experiments to demonstrate telepresence control of an underwater remotely operated vehicle (TROV) to perform scientific field work in isolated and hostile environments. Toward this end, we have developed a telepresence control system and interfaced it to an underwater remotely operated vehicle. This vehicle was used during 1992 to study aquatic ecosystems in Antarctica including a study of the physical and biological environment of permanently ice-covered lake. We also performed a preliminary analysis of the potential for using the TROV to study the benthic ecology under the sea ice in McMurdo sound. These expeditions are opening up new areas of research by using telepresence control of remote vehicles to explore isolated and extreme environments on Earth while also providing an impetus to develop technology which will play a major role in the human exploration of Mars. Antarctic field operations, in particular, provide an excellent analog experience for telepresence operation in space

Global analysis of muon decay measurements

We have performed a global analysis of muon decay measurements to establish model-independent limits on the space-time structure of the muon decay matrix element. We find limits on the scalar, vector and tensor coupling of right- and left-handed muons to right- and left-handed electrons. The limits on those terms that involve the decay of right-handed muons to left-handed electrons are more restrictive than in previous global analyses, while the limits on the other non-standard model interactions are comparable. The value of the Michel parameter eta found in the global analysis is -0.0036 \pm 0.0069, slightly more precise than the value found in a more restrictive analysis of a recent measurement. This has implications for the Fermi coupling constant G_F.Comment: 5 pages, 3 table