Gyroremanent magnetization produced by specimen rotation between successive alternating field treatments     

J. Edwards 《Geophysical Journal International》1982,71(1):199-214

Summary. On the basis of existing theories of rotational remanent magnetization, it is predicted that a gyroremanent magnetization (GRM) might be induced in an isotropic specimen whose orientation is changed during the interval between successive alternating field treatments. An expression is derived, relating the relative magnitude of GRM to the angular displacement, θ of a specimen about an axis perpendicular to the alternating field axis. The predicted effects were observed for four of the five specimens investigated, and in each case GRM was of comparable magnitude to the corresponding partial rotational remanent magnetization. Hysteresis loop curves and characteristics are all consistent with a main magnetic component comprising magnetite grains. A possible connection between GRM and another form of GRM reported in the case of an anisotropic specimen is suggested. Demagnetization of isotropic (and anisotropic) samples by means of the multi-axis technique might be adversely affected by production of GRM.  相似文献   

A Comparison between Etched Fission Track Densities on Internal and External Glass Surfaces after Neutron Irradiation     

J. Edwards 《Geophysical Journal International》1967,13(5):541-543

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An experiment relating to rotational remanent magnetization and frequency of demagnetizing field     

J. Edwards 《Geophysical Journal International》1980,60(2):283-288

Summary. Several tests have been carried out to investigate how the generation of rotational remanent magnetization depended on the frequency of the applied demagnetizing field. The equipment used is described. The investigation was carried out using two specimens, one being a synthetic specimen of magnetite, and the other a cylindrical rock sample. These specimens gave virtually identical behaviour with varying frequency, unlike the differing behaviours reported previously by Wilson & Lomax. For each of the separate alternating field frequencies used (ranging from 50 to 1210 Hz), as the rotational speed of each specimen was reduced from 0.1 cycle s⁻¹, the corresponding rotational remanent magnetization increased to a maximum value when the rotational speed was in each case just a little greater than 0.01 cycle s⁻¹, after which the rotational remanence decreases as the rotational speed decreases.  相似文献   

Comparisons between the generation and properties of rotational remanent magnetization and anhysteretic remanent magnetization     

J. Edwards 《Geophysical Journal International》1980,62(2):379-392

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Bistability of the thermohaline circulation identified through comprehensive 2-parameter sweeps of an efficient climate model   总被引：2，自引：0，他引：2  

R. Marsh  A. Yool  T. M. Lenton  M. Y. Gulamali  N. R. Edwards  J. G. Shepherd  M. Krznaric  S. Newhouse  S. J. Cox 《Climate Dynamics》2004,23(7-8):761-777

The effect of changes in zonal and meridional atmospheric moisture transports on Atlantic overturning is investigated. Zonal transports are considered in terms of net moisture export from the Atlantic sector. Meridional transports are related to the vigour of the global hydrological cycle. The equilibrium thermohaline circulation (THC) simulated with an efficient climate model is strongly dependent on two key parameters that control these transports: an anomaly in the specified Atlantic–Pacific moisture flux (F_a) and atmospheric moisture diffusivity (K_q). In a large ensemble of spinup experiments, the values of F_a and K_q are varied by small increments across wide ranges, to identify sharp transitions of equilibrium THC strength in a 2-parameter space (between Conveyor On and Off states). Final states from this ensemble of simulations are then used as the initial states for further such ensembles. Large differences in THC strength between ensembles, for identical combinations of F_a and K_q, reveal the co-existence of two stable THC states (Conveyor On and Off)—i.e. a bistable regime. In further sensitivity experiments, the model is forced with small, temporary freshwater perturbations to the mid-latitude North Atlantic, to establish the minimum perturbation necessary for irreversible THC collapse in this bistable regime. A threshold is identified in terms of the forcing duration required. The model THC, in a Conveyor On state, irreversibly collapses to a Conveyor Off state under additional freshwater forcing of just 0.1 Sv applied for around 100 years. The irreversible collapse is primarily due to a positive feedback associated with suppressed convection and reduced surface heat loss in the sinking region. Increased atmosphere-to-ocean freshwater flux, under a collapsed Conveyor, plays a secondary role.  相似文献   

The Global Paleomonsoon as seen through speleothem records from Asia and the Americas   总被引：3，自引：0，他引：3  

Hai Cheng  Ashish Sinha  Xianfeng Wang  Francisco W. Cruz  R. Lawrence Edwards 《Climate Dynamics》2012,39(5):1045-1062

The regional monsoons of the world have long been viewed as seasonal atmospheric circulation reversal—analogous to a thermally-driven land-sea breeze on a continental scale. This conventional view of monsoons is now being integrated at a global scale and accordingly, a new paradigm has emerged which considers regional monsoons to be manifestations of global-scale seasonal changes in response to overturning of atmospheric circulation in the tropics and subtropics, and henceforth, interactive components of a singular Global Monsoon (GM) system. The paleoclimate community, however, tends to view ‘paleomonsoon’ (PM), largely in terms of regional circulation phenomena. In the past decade, many high-quality speleothem oxygen isotope (δ¹⁸O) records have been established from the Asian Monsoon and the South American Monsoon regions that primarily reflect changes in the integrated intensities of monsoons on orbital-to-decadal timescales. With the emergence of these high-resolution and absolute-dated records from both sides of the Equator, it is now possible to test a concept of the ‘Global-Paleo-Monsoon’ (GPM) on a wide-range of timescales. Here we present a comprehensive synthesis of globally-distributed speleothem δ¹⁸O records and highlight three aspects of the GPM that are comparable to the modern GM: (1) the GPM intensity swings on different timescales; (2) their global extent; and (3) an anti-phased inter-hemispheric relationship between the Asian and South American monsoon systems on a wide range of timescales.  相似文献   

Radiative Processes in the Stable Boundary Layer: Part I. Radiative Aspects   总被引：1，自引：0，他引：1  

J. M. Edwards 《Boundary-Layer Meteorology》2009,132(2):349-350

The structure of the radiatively dominated stable boundary layer is analysed using idealized calculations at high vertical and spectral resolution. The temperature profile of a nocturnal radiative boundary layer, developing after the evening transition, is found to be well described in terms of radiative cooling to the surface, although radiative exchanges within the atmosphere become increasingly important with time. The treatment of non-black surfaces is discussed in some detail and it is shown that the effect of reducing the surface emissivity is to decrease rather than to increase the radiative cooling rate in the surface layer. It is also argued that an accurate assessment of the impact of non-black surfaces requires careful attention to the spectral and directional characteristics of the surface emissivity. A polar nocturnal boundary layer, developing above snow-covered ground, is simulated and found to reach a slowly evolving state characterized by a strong radiative divergence near the surface that is comparable to observed values. Radiative boundary layers are characterized by large temperature gradients near the surface. An erratum to this article can be found at  相似文献   

Assessment of Raman spectroscopy as a tool for the non-destructive identification of organic minerals and biomolecules for Mars studies     

J. Jehlička  H.G.M. Edwards  P. Vítek 《Planetary and Space Science》2009,57(5-6):606-613

Several characteristic geological features found on the surface of Mars by planetary rovers suggest that a possible extinct biosphere could exist based on similar sources of energy as occurred on Earth. For this reason, analytical instrumental protocols for the detection of biomarkers in suitable geological matrices unequivocally have to be elaborated for future unmanned explorations including the forthcoming ESA ExoMars mission. As part of the Pasteur suite of analytical instrumentation on ExoMars, the Raman/LIBS instrument will seek elemental and molecular information about geological, biological and biogeological markers in the Martian record. A key series of experiments on terrestrial Mars analogues, of which this paper addresses a particularly important series of compounds, is required to obtain the Raman spectra of key molecules and crystals, which are characteristic for each biomarker. Here, we present Raman spectra of several examples of organic compounds which have been recorded non-destructively—higher n-alkanes, polycyclic aromatic hydrocarbons, carotenoids, salts of organic acids, pure crystalline terpenes as well as oxygen-containing organic compounds. In addition, the lower limit of β-carotene detection in sulphate matrices using Raman microspectroscopy was estimated.  相似文献   

The diverse nature of optical emission lines in brightest cluster galaxies: IFU observations of the central kiloparsec     

Louise O. V. Edwards †  Carmelle Robert  Mercedes Mollá  Sean L. McGee 《Monthly notices of the Royal Astronomical Society》2009,396(4):1953-1971

We present integral field spectroscopy of the nebular line emission in a sample of nine brightest cluster galaxies (BCGs). The sample was chosen to probe both cooling flow and non-cooling flow clusters, as well as a range of cluster X-ray luminosities. The line emission morphology and velocity gradients suggest a great diversity in the properties of the line emitting gas. While some BCGs show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and MKW 3s), others have extended emission (Abell 1204, Abell 2199), while still others have centrally concentrated emission (Abell 2052). We examine diagnostic line ratios to determine the dominant ionization mechanisms in each galaxy. Most of the galaxies show regions with active galactic nucleus like spectra, however, for two BCGs, Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which can be described by the emission from young stellar populations. The diversity of emission-line properties in our sample of BCGs suggests that the emission mechanism is not universal, with different ionization processes dominating different systems. Given this diversity, there is no evidence for a clear distinction of the emission-line properties between cooling flow and non-cooling flow BCGs. It is not always cooling flow BCGs which show emission (or young stellar populations), and non-cooling flow BCGs which do not.  相似文献   

Isolation,biodegradation ability and molecular detection of hydrocarbon degrading bacteria in petroleum samples from a Brazilian offshore basin     

Suzan Pantaroto de Vasconcellos  Elaine Crespim  Georgiana Feitosa da Cruz  Diego Barbosa Senatore  Karen Christina Marques Simioni  Eugênio Vaz dos Santos Neto  Anita Jocelyne Marsaioli  Valéria Maia de Oliveira 《Organic Geochemistry》2009,40(5):574-588

The detection of microorganisms with potential for biodeterioration and biodegradation in petroleum fields is of great relevance, since these organisms may be related to a decrease in petroleum quality in the reservoirs or damage in the production facilities. In this sense, petroleum formation water and oil samples were collected from the Campos Basin, Brazil, with the aim of isolating microorganisms and evaluating their ability to degrade distinct classes of hydrocarbon biomarkers (9,10-dihydrophenanthrene, phytane, nonadecanoic acid and 5α-cholestane). Twenty eight bacterial isolates were recovered and identified by sequencing their 16S rRNA genes. Biodegradation assays revealed that bacterial metabolism of hydrocarbons occurred through reactions based on oxidation, carbon–carbon bond cleavage and generation of new bonds or by the physical incorporation of hydrocarbons into microbial cell walls. Based on the biodegradation results, selective PCR-based systems were developed for direct detection in petroleum samples of bacterial groups of interest, namely Bacillus spp., Micrococcus spp., Achromobacter xylosoxidans, Dietzia spp. and Bacillus pumilus. Primer sets targeting 16S rRNA genes were designed and their specificity was confirmed in silico (i.e. computational analysis) and in PCR reactions using DNA from reference strains as positive and negative controls. Total DNA from oil was purified and the amplification tests revealed the presence of the target bacteria in the samples, unraveling a significant potential for petroleum deterioration in the reservoirs sampled, once proper conditions are present for hydrocarbon degradation. The application of molecular methods for rapid detection of specific microorganisms in environmental samples would be valuable as a supporting tool for the evaluation of oil quality in production reservoirs.  相似文献