A Brief History of Star Formation and Chemical Enrichment in the Bulge of the Milky way

Observations of the stellar content of the bulge of the Milky Way can provide critical guidelines for the interpretation of observations of distant galaxies, in particular for understanding their stellar content and evolution. In this brief overview I will first highlight some recent work directed towards measuring the history of star formation and the chemical composition of the central few parsecs of the Galaxy. These observations point to an episodic history of star formation in the central region with several bursts having occurred over the past few 100 Myr (e.g. Blum et al., 1996b). High resolution spectroscopic observations by Ramírez et al. (1998) of luminous M stars in this region yield a near solar value for [Fe/H] from direct measurements of iron lines. Then I will present some results from an ongoing program by my colleagues and myself the objective of which is the delineation of the star formation and chemical enrichment histories of the central 100 parsecs of the Galaxy, the `inner bulge'. From new photometric data we have concluded that there is a small increase in mean [Fe/H] from Baade's Window to the Galactic Center and deduce a near solar value for stars in the central region. For radial distances greater than 1^° from the Galactic Center we fail to find a measurable population of stars that are significantly younger than those in Baade's Window. Within 1^° we find a number of luminous M giants that most likely are the result of a star formation episode not more than one or two Gyr ago. This revised version was published online in July 2006 with corrections to the Cover Date.     

Late Jurassic subsidence and passive margin evolution in the Vulcan Sub-basin, north-west Australia: constraints from basin modelling

The Vulcan Sub-basin, located in the Timor Sea, north-west Australia, developed during the Late Jurassic extension which ultimately led to Gondwanan plate breakup and the development of the present-day passive continental margin. This paper describes the evolution of upper crustal extension and the development of Late Jurassic depocentres in this subbasin, via the use of forward modelling techniques. The results suggest that a lateral variation in structural style exists. The south of the basin is characterized by relatively large, discrete normal faults which have generated deep sub-basins, whereas more distributed, small-scale faulting further north reflects a collapse of the early basin margin, with the development of a broader, 'sagged' basin geometry. By combining forward and reverse modelling techniques, the degree of associated lithosphere stretching can be quantified. Upper crustal faulting, which represents up to 10% extension, is not balanced by extension in the deeper, ductile lithosphere; the magnitude of this deeper extension is evidenced by the amount of post-Valanginian thermal subsidence. Reverse modelling shows that the lithosphere stretching
factor has a magnitude of up to β=1.55 in the southern Vulcan Sub-basin, decreasing to β=1.2 in the northern Vulcan Sub-basin. It is proposed that during plate breakup, deformation in the Vulcan Sub-basin consisted of depth-dependent lithosphere extension. This additional component of lower crustal and lithosphere stretching is considered to reflect long-wavelength partitioning of strain associated with continental breakup, which may have extended 300–500 km landward of the continent–ocean boundary.     

A complete sample of radio sources in the North Ecliptic Cap, selected at 38 MHz – III. Further imaging observations and the photometric properties of the sample

Further imaging observations of a sample of radio sources in the North Ecliptic Cap are presented and a number of new identifications are made. Using redshifts from spectroscopic data presented in a companion paper by Lacy et al., the photometric properties of the galaxies in the sample are discussed. It is shown that: (1) out to at least z ≈0.6 radio galaxies are good standard candles irrespective of radio luminosity; (2) for 0.6≲ z ≲1 a large fraction of the sample has magnitudes and colours consistent with a non-evolving giant elliptical, and (3) at higher redshifts, where the R -band samples the rest-frame UV flux, most objects have less UV luminosity than expected if they form their stellar populations at a constant rate from a high redshift to z ∼1 in unobscured star-forming regions (assuming an Einstein–de Sitter cosmology). The consequences of these observations are briefly discussed.     

Can we predict the future food production? A sensitivity analysis

An attempt is made to assess the sensitivity of food production to various aspects of global change and environmental degradation during the next few decades. As a tool for this study a spreadsheet accounting system for food demand and supply is used. Taking into account the uncertainties of the various influencing factors, such as new technologies, improved management, increased fertilizer use, climatic change, expansion of irrigation, soil degradation and loss of agricultural land, the study indicates that one cannot say with any certainty whether or not food supply will meet expected demand in 2025, especially in Less Developed Countries. Bringing into use 10% of available potential cropland will make little difference.     

Uncertainty and sensitivity in a bank stability model: implications for estimating phosphorus loading

Eutrophication of aquatic ecosystems is one of the most pressing water quality concerns in the United States and around the world. Bank erosion has been largely overlooked as a source of nutrient loading, despite field studies demonstrating that this source can account for the majority of the total phosphorus load in a watershed. Substantial effort has been made to develop mechanistic models to predict bank erosion and instability in stream systems; however, these models do not account for inherent natural variability in input values. To quantify the impacts of this omission, uncertainty and sensitivity analyses were performed on the Bank Stability and Toe Erosion Model (BSTEM), a mechanistic model developed by the US Department of Agriculture – Agricultural Research Service (USDA‐ARS) that simulates both mass wasting and fluvial erosion of streambanks. Generally, bank height, soil cohesion, and plant species were found to be most influential in determining stability of clay (cohesive) banks. In addition to these three inputs, groundwater elevation, stream stage, and bank angle were also identified as important in sand (non‐cohesive) banks. Slope and bank height are the dominant variables in fluvial erosion modeling, while erodibility and critical shear stress had low sensitivity indices; however, these indices do not reflect the importance of critical shear stress in determining the timing of erosion events. These results identify important variables that should be the focus of data collection efforts while also indicating which less influential variables may be set to assumed values. In addition, a probabilistic Monte‐Carlo modeling approach was applied to data from a watershed‐scale sediment and phosphorus loading study on the Missisquoi River, Vermont to quantify uncertainty associated with these published results. While our estimates aligned well with previous deterministic modeling results, the uncertainty associated with these predictions suggests that they should be considered order of magnitude estimates only. Copyright © 2016 John Wiley & Sons, Ltd.     

Some Uncertainties in the Derivation of Rates of Denudation from Thermochronologic Data

Low-temperature thermochronology, such as that provided by apatite fission-track analysis, provides a valuable means of establishing the timing of major denudational events and associated rates of denudation over geological time-scales of 10⁶–10⁸ Ma. Care must be taken, however, in deriving denudation rates from the crustal cooling histories documented by thermochronologic techniques, especially in rapidly eroding terrains, since, in such cases, apparent denudation rates derived from thermochronologic data will usually overestimate true rates if the advective effect of denudation is not included. This is likely to be resolvable where the rate of denudation exceeds 300 m Ma⁻¹ and when the depth of denudation occurring at these rates exceeds several kilometres prior to the sample cooling below the appropriate closure temperature. Because the time at which a sample cools below a particular closure temperature is relatively insensitive to advection, the initiation of denudation can be accurately established, even given uncertainties in the estimation of depths and rates of denudation. Where thermal events originate from a source within or below the lower crust, the cooling through denudation will dominate the low-temperature history of the shallow crust if denudation occurs coevally with the subsurface heating. © 1997 by John Wiley & Sons, Ltd.     

The value of multiple earthquake missions: the EEFIT L’Aquila Earthquake experience

In November 2012 EEFIT launched its first ever return mission to an earthquake affected site. The L’Aquila Earthquake site was chosen as this is a recent European event of interest to the UK and European earthquake engineering community. The main aims of this return mission were to document the earthquake recovery process and this paper presents an overview of the post-disaster emergency phase and transition to reconstruction in the Aquila area after the earthquake. It takes an earthquake engineering perspective, highlighting areas mainly of interest to the fields of structural/seismic engineering and reconstruction management. Within the paper, reference is made to published literature, but also to data collected in the field during the return mission that would not otherwise have been available. The paper presents some specific observations and lessons learned from the L’Aquila return mission. However, in light of current international efforts in conducting return missions, the paper ends with some reflections on the value that return missions can provide to the field of earthquake engineering in general, based on the EEFIT L’Aquila experience.