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Certain geological features have been interpreted as evidence of channelized magma flow in the mantle, which is a compacting porous medium. Aharonov et al. (J. Geophys. Res., vol. 100 (B10), 1995, pp. 20433–20450) developed a simple model of reactive porous flow and numerically analysed its instability to channels. The instability relies on magma advection against a chemical solubility gradient and the porosity-dependent permeability of the porous host rock. We extend the previous analysis by systematically mapping out the parameter space. Crucially, we augment numerical solutions with asymptotic analysis to better understand the physical controls on the instability. We derive scalings for the critical conditions of the instability and analyse the associated bifurcation structure. We also determine scalings for the wavelengths and growth rates of the channel structures that emerge. We obtain quantitative theories for and a physical understanding of, first, how advection or diffusion over the reactive time scale sets the horizontal length scale of channels and, second, the role of viscous compaction of the host rock, which also affects the vertical extent of channelized flow. These scalings allow us to derive estimates of the dimensions of emergent channels that are consistent with the geologic record.
Introduction: Understanding factors associated with increased use of nicotine replacement therapy (NRT) is critical to implementing cessation interventions for low-income individuals yet the factors associated with NRT use among low-income smokers are poorly understood.
Aims: Assess factors associated with NRT use among low-income public housing residents.
Methods: ‘Kick it for Good’ was a randomised smoking cessation intervention study conducted among residents of public housing sites in Boston, MA. Secondary, cross-sectional analyses were conducted on smokers from a community-based intervention cessation intervention who reported making a quit attempt and use of NRT in the past 12 months (n = 234).
Results: Among smokers who made a quit attempt in the past year, 29% reported using NRT. Black (prevalence ratio, PR = 0.52, 95% CI: 0.38–0.71) and Hispanic (PR = 0.52, 95% CI: 0.31–0.88) participants were less likely to report use of NRT compared with Whites. The prevalence of recent NRT use was greatest among those both asking for and receiving provider advice (PR = 1.90, 95% CI: 0.96–3.78).
Conclusions: Minority race and ethnicity and low provider engagement on NRT use were associated with lower NRT use. Providing barrier-free access to NRT and facilitating provider engagement with smokers regarding NRT use can increase NRT use among low-income populations.
Mitochondrial dysfunction and resulting changes in adiposity have been observed in the offspring of animals fed a high fat (HF) diet. As iron is an important component of the mitochondria, we have studied the offspring of female rats fed complete (Con) or iron-deficient (FeD) rations for the duration of gestation to test for similar effects. The FeD offspring were ~12% smaller at weaning and remained so because of a persistent reduction in lean tissue mass. The offspring were fed a complete (stock) diet until 52 weeks of age after which some animals from each litter were fed a HF diet for a further 12 weeks. The HF diet increased body fat when compared with animals fed the stock diet, however, prenatal iron deficiency did not change the ratio of fat:lean in either the stock or HF diet groups. The HF diet caused triglyceride to accumulate in the liver, however, there was no effect of prenatal iron deficiency. The activity of the mitochondrial electron transport complexes was similar in all groups including those challenged with a HF diet. HF feeding increased the number of copies of mitochondrial DNA and the prevalence of the D-loop mutation, however, neither parameter was affected by prenatal iron deficiency. This study shows that the effects of prenatal iron deficiency differ from other models in that there is no persistent effect on hepatic mitochondria in aged animals exposed to an increased metabolic load.
Glaciers and ice caps around the world are changing quickly, with surge-type behaviour superimposed upon climatic forcing. Here, we study Iceland's second largest ice cap, Langjökull, which has both surge- and non-surge-type outlets. By differencing elevation change with surface mass balance, we estimate the contribution of ice dynamics to elevation change. We use DEMs, in situ stake measurements, regional reanalyses and a mass-balance model to calculate the vertical ice velocity. Thus, we not only compare the geodetic, modelled and glaciological mass balances, but also map spatial variations in glacier dynamics. Maps of emergence and submergence velocity successfully highlight the 1998 surge and subsequent quiescence of one of Langjökull's outlets by visualizing both source and sink areas. In addition to observing the extent of traditional surge behaviour (i.e. mass transfer from the accumulation area to the ablation area followed by recharge of the source area), we see peripheral areas where the surge impinged upon an adjacent ridge and subsequently retreated. While mass balances are largely in good agreement, discrepancies between modelled and geodetic mass balance may be explained by inaccurate estimates of precipitation, saturated adiabatic lapse rate or degree-day factors. Nevertheless, the study was ultimately able to investigate dynamic surge behaviour in the absence of in situ measurements during the surge.
We present new local groundwater-level rise data from two Late Glacial aeolian dunes, located near Barendrecht and Oud-Alblas in the western Rhine-Meuse delta. These data are based on AMS radiocarbon dating of terrestrial macrofossils, collected from the base of peat formed on the slopes of these dunes. This method avoids contamination of bulk peat samples by old soil carbon or younger rootlets and rhizomes, as well as the hardwater effect. The new data are used to assess the reliability of previously published groundwater-level index data based on conventional radiocarbon dating of bulk basal peat samples from the slopes of the Late Glacial aeolian dunes at Barendrecht, Hillegersberg, Bolnes and Wijngaarden, all located in the western Rhine-Meuse delta.
Comparison of the new and published groundwater-level data shows no significant systematic difference between conventionally dated bulk peat samples and AMS-dated samples of terrestrial macrofossils. The new data from the dune at Barendrecht confirm the reliability of the younger than 6600 cal yr BP age-depth data from the dunes at Hillegersberg and near Bolnes. This result supports the validity of this part of the mean sea-level (MSL) curve for the western Netherlands. Consequently, the position of the groundwater-level curve for Flevoland (central Netherlands) below this MSL curve can most likely be attributed to differential land-level movement.
The available data show that the groundwater-gradient effect in the western Rhine-Meuse delta became less than 5 cm/km after 6600 cal yr BP. Finally, temporal correlation between temporary increases in local groundwater-level rise with known shifts of river courses in the delta plain suggests, that avulsions can explain sudden local deviations from the trend in groundwater-level rise. A general conclusion of this study is that a complex relationship exists between sea level and local delta-plain water levels.
The free-boundary problem between a liquid region and a mushy layer (a reactive porous medium) must respect both thermodynamic and fluid dynamical considerations. We develop a steady two-dimensional forced-flow configuration to investigate the thermodynamic condition of marginal equilibrium that applies to a solidifying mushy layer with outflow and requires that streamlines are tangent to isotherms at the interface. We show that a ‘two-domain’ approach in which the mushy layer and liquid region are distinct domains is consistent with marginal equilibrium by extending the Stokes equations in a narrow transition region within the mushy layer. We show that the tangential fluid velocity changes rapidly in the transition region to satisfy marginal equilibrium. In convecting mushy layers with liquid channels, a buoyancy gradient can drive this tangential flow. We use asymptotic analysis in the limit of small Darcy number to derive a regime diagram for the existence of steady solutions. Thus we show that marginal equilibrium is a robust boundary condition and can be used without precise knowledge of the fluid flow near the interface.
This editorial proposes a shift in emphasis in the field of mental health epidemiology in conflict-affected settings. After a brief summary of the nature of contemporary armed conflicts, we consider the current and potential roles that epidemiology can play with regard to: (1) establishing the burden of mental disorders; (2) identifying risk and protective factors; and (3) intervention research. We advocate for improved methodological rigor; more attention to mixed methods approaches and multi-level longitudinal research; inclusion of the determinants of mental health beyond conflict-related violence; and consideration of a wider array of mental health outcomes. We particularly highlight the importance of expanding interest to epidemiological research that advances prevention and promotion interventions (e.g., in the early childhood period), in order to fill the gap between epidemiology and mental health practice in conflict-affected settings.
Solute transport within solidifying binary alloys occurs predominantly by convection from narrow liquid chimneys within a porous mushy layer. We develop a simple model that elucidates the dominant structure and driving forces of the flow, which could be applied to modelling brine fluxes from sea ice, where a cheaply implementable approach is essential. A horizontal density gradient within the mushy layer in the vicinity of the chimneys leads to baroclinic torque which sustains the convective flow. In the bulk of the mushy layer, the isotherms are essentially horizontal. In this region, we impose a vertically linear temperature field and immediately find that the flow field is a simple corner flow. We determine the strength of this flow by finding a similarity solution to the governing mushy-layer equations in an active region near the chimney. We also determine the corresponding shape of the chimney, the vertical structure of the solid fraction and the interstitial flow field. We apply this model first to a periodic, planar array of chimneys and show analytically that the solute flux through the chimneys is proportional to a mush Rayleigh number. Secondly we extend the model to three dimensions and find that an array of chimneys can be characterized by the average drainage area alone. Therefore we solve the model in an axisymmetric geometry and find new, sometimes nonlinear, relationships between the solute flux, the Rayleigh number and the other dimensionless parameters of the system.
In Chapter 3 we discussed principally the interaction of electromagnetic radiation with the surface and bulk of the material being sensed. However, the radiation also has to make at least one journey through at least part of the Earth's atmosphere, and two such journeys in the case of systems that detect reflected radiation, whether artificial or naturally occurring. Each time radiation passes through the atmosphere it is attenuated to some extent. In addition, as we have already seen in Section 3.1.2 and Figure 3.5, the atmosphere has a refractive index that differs from unity so that radiation travels through it at a speed different from the free-space speed of 299 792 458 m s−1. These phenomena must be considered if the results of a remotely sensed measurement are to be corrected for the effects of atmospheric propagation, or if they are to be used to infer the properties of the atmosphere itself. We have already considered them in general terms in discussing the radiative transfer equation (Section 3.4). In this chapter we shall relate them more directly to the constituents of the atmosphere.
Composition and structure of the gaseous atmosphere
At sea level, the principal constituents of the dry atmosphere are molecules of nitrogen (about 78% by volume), oxygen (21%) and the inert gas argon (1%). There is also a significant but variable (typically 0.1% to 3%) amount of water vapour, often specified by the relative humidity H.
Fully updated and containing significant new material on photography, laser profiling and image processing, the third edition of this popular textbook covers a broad range of remote sensing applications and techniques across the Earth, environmental and planetary sciences. It focuses on physical principles, giving students a deeper understanding of remote sensing systems and their possibilities, while remaining accessible to those with less mathematical training by providing a step-by-step approach to quantitative topics. Boxed examples, additional photos and numerous colour images engage students and show them how the theory relates to the many real-world applications. Chapter summaries, review questions and additional problems allow students to check their understanding of key concepts and practise handling real data for themselves. Supplementary online material includes links to freely available software, animations, computer programs, colour images and other web-based resources of interest.
There are many books that explain the subject of remote sensing to those whose backgrounds are primarily in the environmental sciences. This is an entirely reasonable fact, since they continue to be the main users of remotely sensed data. However, as the subject grows in importance, the need for a significant number of people to understand not only what remote sensing systems do, but how they work, will grow with it. This was already happening in 1990, when the first edition of Physical Principles of Remote Sensing appeared, and since then increasing numbers of physical scientists, engineers and mathematicians have moved into the field of environmental remote sensing. It is mainly for such readers that this book, like its previous editions, has been written. That is to say, the reader for whom I have imagined myself to be writing is educated to a reasonable standard (although not necessarily to first degree level) in physics, with a commensurate mathematical background. I have however found it impossible to be strictly consistent about this, because of the wide range of disciplines within and beyond physics from which the material has been drawn, and I trust that readers will be understanding when they find the treatment either too simple or over their heads.
In Chapter 1 we noted that electromagnetic radiation is fundamental to remote sensing as we have defined it: the information about the sensed object is carried by this radiation. We therefore need to develop an understanding of the essential characteristics of this radiation and of how it interacts with its surroundings. This is a large topic and it is covered in this chapter and the next two. In this chapter we consider electromagnetic radiation in its simplest form, when it is propagating in (travelling through) a vacuum, usually termed ‘free space’. This is practically useful, because for much of its journey towards the sensor the radiation is propagating in a medium that approximates to free space, and it also allows us to develop some of the essential ideas that describe electromagnetic radiation without too much confusing detail.
A particularly important part of this chapter deals with thermal radiation. As we noted in Chapter 1, most passive remote sensing systems detect thermal radiation (in the infrared or microwave regions) or they detect reflected solar radiation. Solar radiation is itself, as explained in this chapter, essentially just another form of thermal radiation, so by developing an understanding of thermal radiation we are able to describe many of the characteristics of the radiation detected by passive systems.
In Chapter 5 we discussed photographic systems, and although these provide a familiar model for many of the concepts to be addressed in this and subsequent chapters, they nevertheless stand somewhat apart from the types of system to be discussed in Chapters 6 to 9. In the case of photographic systems, the radiation is detected through a photochemical process, whereas in the systems we shall now consider it is converted into an electronic signal that can be detected, amplified and subsequently further processed electronically. This clearly has many advantages, not least of which is the comparative simplicity with which the data may be transmitted as a modulated radio signal, recorded digitally and processed in a computer.
In this chapter, we shall consider electro-optical systems, interpreted fairly broadly to include the visible, near-infrared and thermal infrared regions of the electromagnetic spectrum. The reason for this is a pragmatic one, since many instruments combine a response in the visible and near infrared (VNIR) region with a response in the thermal infrared (TIR) region, and much of the technology is common to both. Within this broad definition we shall distinguish imaging systems, designed to form a two-dimensional representation of the two-dimensional distribution of radiance across the target, and systems used for profiling the properties and contents of the atmosphere. It is clear that an imaging system operating in the VNIR region has much in common with aerial photography, and systems of this type are in very wide use from both airborne and spaceborne platforms. We shall therefore begin our discussion with these systems.
‘Remote sensing’ is, broadly but logically speaking, the collection of information about an object without making physical contact with it. (The term was coined by Evelyn Pruitt of the US Office of Naval Research in the 1950s.) This is a simple definition, but too vague to be really useful (Campbell 2008), so for the purpose of this book we restrict it by confining our attention to the Earth’s surface and atmosphere, viewed from above using electromagnetic radiation. This narrower definition excludes such techniques as seismic, geomagnetic and sonar investigations, as well as (for example) medical and planetary imaging, all of which could otherwise reasonably be described as remote sensing, but it does include a broad and reasonably coherent set of techniques, nowadays often described by the alternative name of Earth observation. These techniques, which now have a huge range of applications in the ‘civilian’ sphere as well as their obvious military uses, make use of information impressed in some way on electromagnetic radiation ranging from ultraviolet to radio frequencies.
One important casualty of our restricted definition of remote sensing is the use of spaceborne methods of measuring the Earth’s gravitational field. Although observations from artificial Earth satellites have been used since the 1970s to measure the Earth’s gravity, our current (at the time of writing, in 2012) ability in this regard is a remarkable indication of the level of space technology. This is the GRACE (Gravity Recovery and Climate Experiment) mission, launched in 2002. Two satellites, each with a mass of around half a tonne, follow the same orbit 500 km above the Earth’s surface. They are approximately 220 km apart, and the distance between them is constantly monitored with an accuracy of 10 µm. This distance changes as the satellites cross regions of different gravitational field strength. The GRACE system is sensitive enough to respond to changes in groundwater in a large river basin. Data from the GRACE mission are described in Chapter 8.
The interaction of electromagnetic radiation with matter is evidently fundamental to remote sensing. The subject is a vast one, embracing many areas of physics, and a fully systematic treatment of it would require at least a book in itself. In this chapter, therefore, we attempt to provide an overview that will be sufficient to gain an understanding of the operation of remote sensing systems. In order to keep the chapter to a manageable length, we reserve a discussion of the interaction of electromagnetic radiation with the Earth’s atmosphere to Chapter 4. Nevertheless, this is still a long chapter, and it is also the most technical in the book. It is not necessary to understand all of the material in this chapter in order to follow the subsequent material but, as usual, a reading of the summaries at the end of each section should give a general understanding of the material.
The chapter first extends some of the concepts of Chapter 2 into a consideration of how electromagnetic radiation propagates in homogeneous dielectric media. The key concepts here are the dielectric constant (also known as the relative electric permittivity) and the refractive index. By allowing these parameters to take complex, rather than purely real, values, the concept of absorption of radiation is included, and by allowing them to vary with frequency (or equivalently with wavelength) we are able to include the idea of dispersion, which will be important in Chapter 8 where we consider ranging systems.