Near-future changes in storm surges along the Atlantic Iberian coast

Natural Hazards - Decadal predictions bridge the gap between the short-term weather/seasonal forecasts and the long-term climate projections. They target the reproduction of large-scale weather...     

Orientation dependence of luminescence in plagioclase

The orientation dependence of the luminescence of a well-characterized plagioclase crystal at room temperature and 40 K is reported. A beam of H ⁺ ions was used to provide the excitation. Ion beam luminescence provides emissions effectively from the bulk of the material, and therefore minimizes the contribution to the luminescence from atypical regions. The intensity of the luminescence is strongly orientation-dependent. The intensity and photon energy, particularly of the red/infrared and yellow emission bands, vary significantly. We interpreted this as resulting from Fe ³⁺ and Mn ²⁺ activator ions, respectively, on crystallographic sites with low point symmetry. An emission at 860 nm was also significantly orientation-dependent. The blue luminescence showed the least variability. At room temperature, a 350 nm near-UV emission was noted, whereas at 40 K, emissions were at 240, 260, 300 and 340 nm. UV emissions may result from Na ⁺ diffusion along interfaces within the plagioclase, notably albite-law (010) twins. This variability has significant consequences for the use of single-crystal quantitative luminescence techniques. We have also studied the dependence of the peak intensities and profiles during prolonged ion beam bombardment with heavier (He ⁺) ions. Broadening of the red-infrared emission is interpreted as reflecting growing amorphization of the sample.     

The red to near-infrared luminescence in alkali feldspar

Results are presented for the radio-, cathodo- and ionoluminescence (RL, CL and IL) of an ordered, exsolved alkali feldspar from South Greenland (BM2). BM2, a microperthite typical of many evolved rocks, has a broad red near-infrared luminescence, which, using lifetime-resolved CL, reveals four overlapping emissions, of which two are dominant. These derive from Fe³⁺-activated luminescence from the low albite and maximum microcline components of the microperthite in which the Fe is on the most ordered tetrahedral site. The temperature dependence of the emission shows a smooth change from longer wavelengths at 20 K to shorter values at room temperature. There is a broad relationship between Fe-O bond distance and the energy of the luminescence. Comparisons of RL, CL and IL allow features in the luminescence associated with surface states to be identified. The dependence of red RL intensity versus temperature is divided into four regions for which the activation energies and temperature ranges are estimated. Variations in RL intensity between 67 and 225 K are interpreted as a phase transition in microcline. RL intensity indicates a multi-stage transformation, proceeding via a first step between 67 and ~100 K in which luminescence intensity increases, followed by a region between 100 and ~225 K in which intensity falls. A discontinuity in intensity at ~225 K marks the end of the second region. These variations may result from changes in the bond angles of bridging oxygens. IL dose dependence studies have been performed. As implantation progresses, the red/IR emission profile skews towards short wavelengths, reflecting amorphisation of the structure and local variations in Fe-O bond distances. If the sample recovers for 24 h, the luminescence profile partly returns to its original state, but remains skewed, reflecting partial resumption of short-range order. Such profiles are also observed from natural shocked feldspars, and it may be that ion beam damage is akin to structural modifications associated with impact events. Ion implantation also causes the formation or enhancement of UV, blue and yellow emissions. Recovery of the sample over 24 h causes the UV and blue emissions to be greatly reduced, whereas the yellow emission may be enhanced. Tentative interpretations of this behaviour are presented.     

GIS for development: a contradiction in terms?

Summary Is it possible to make appropriate use of GIS for 'development' (here defined as change desirable for the poor) in countries where human and financial resources may be limited? We argue that it is, and should be taught, but that there are no quick fixes.     

Field-induced ferromagnetism in minnesotaite

Minnesotaite, a 2:1 layer sheet silicate, is antifer-romagnetic below 30 K. A spin flop or metamagnetic transition occurs in a small applied magnetic field. Neutron diffraction and Mössbauer spectroscopy, in an external magnetic field of 4.0 T, show that the magnetic structure consists of Fe²⁺ spins coupled ferromagnetically in the c plane with alternate ferromagnetic planes coupled antiferromagnetically.     

The distribution and stable carbon isotopic composition of dissolved organic carbon in estuaries

The distributions of dissolved organic carbon (DOC) and the natural carbon isotope ratio of DOC (DO¹³C) in estuaries reflect the predominant sources and sinks of organic matter from both allochthonous and autochthonous origins. The traditional view is that DOC in land-margin ecosystems reflects mainly the mixing of land-derived and oceanic DOC. However, this view is not consistent with the bulk of our data from a survey of DOC and DO¹³C distributions in estuaries on the East and Gulf coasts of the USA. While it is accurate that the DOC in estuaries includes material derived from land and from the ocean, the distributions of DOC and DO¹³C in several estuaries reflect additional DOC inputs from estuarine phytoplankton and tidal marshes. Even when DOC concentrations were distributed conservatively, the isotopic composition of the DOC revealed the existence of a dynamic cycle of DOC input and removal in some systems.     

香港九龙大坑东地下蓄水方案数值研究

香港九龙大坑东地下蓄水方案(Tai Hang Tung Storage Scheme-THTSS)是香港西九龙渠道改善二期计划的一个重要组成部分,其目标是解决香港九龙繁华拥挤、人口稠密的商业中心旺角一带的洪水淹没问题。THTSS即是在经常洪水淹没区域(大坑东和界限街水渠交接处)上游足球场下面建立一个100 000 m3的地下蓄水池。本文建立了一个能处理明渠缓流和急流、封闭管道有压流、侧流堰和渠道汇合处过渡流于一体的一维水力数学模型,用1:22正态物理模型恒定流下的结果进行验证。数值模型计算了在50年一遇暴雨下,非恒定洪水在不同的侧流堰方案下的流动过程。结合物理模型试验结果,选择最佳的地下蓄水方案。计算结果表明,大坑东地下蓄水方案确实能加强旺角地区地洪水控制能力,并能通过50年一遇暴雨的洪水。     

Surface trapping and leakage of low-frequency g modes in rotating early-type stars – I. Qualitative analysis

We summarize all the reported detections of, and upper limits to, the radio emission from persistent (i.e. non-transient) X-ray binaries. A striking result is a common mean observed radio luminosity from the black hole candidates (BHCs) in the low/hard X-ray state and the neutron star Z sources on the horizontal X-ray branch. This implies a common mean intrinsic radio luminosity to within a factor of 25 (or less, if there is significant Doppler boosting of the radio emission). Unless coincidental, these results imply a physical mechanism for jet formation that requires neither a black hole event horizon nor a neutron star surface. As a whole the populations of Atoll and X-ray pulsar systems are less luminous by factors of ≳5 and ≳10 at radio wavelengths than the BHCs and Z sources (while some Atoll sources have been detected, no high-field X-ray pulsar has ever been reliably detected as a radio source). We suggest that all of the persistent BHCs and the Z sources generate, at least sporadically, an outflow with physical dimensions 10¹² cm; that is, significantly larger than the binary separations of most of the systems. We compare the physical conditions of accretion in each of the types of persistent X-ray binary and conclude that a relatively low (10¹⁰ G) magnetic field associated with the accreting object, and a high (0.1 Eddington) accretion rate and/or dramatic physical change in the accretion flow, are required for formation of a radio-emitting outflow or jet.     

Hydropyrolysis as a new tool for radiocarbon pre-treatment and the quantification of black carbon

The first results concerning the potential of hydrogen pyrolysis (hypy) as a new tool for the quantification and isolation of Black Carbon (BC) for radiocarbon analysis are reported. BC is a highly stable form of carbon, produced during pyrolysis of biomass to materials such as charcoal. Isolation and quantification of this component is therefore of great interest in radiocarbon measurement, particularly for more ancient samples, where contamination issues become more critical. Hypy has been demonstrated to reliably separate labile and refractory carbonaceous sample components for engineering and geological applications, but its potential in ¹⁴C geochronological investigation has previously been unexplored. Here, we test the hypy technique using a selection of soil standard samples and ancient charcoals from deposits of geological and archaeological significance. The results show that hypy can effectively and reproducibly isolate different carbon fractions within a variety of sample types and thus has the potential to provide a rapid and robust pre-treatment technique for radiocarbon analysis. Hypy has the additional advantage that the non-BC fraction removed from a sample can be quantitatively collected for subsequent further analysis. The technique represents a promising new approach not only for ensuring reliable decontamination of pyrogenic carbon samples prior to radiocarbon dating, but also for BC quantification in a variety of environmental matrices.