Behaviour,of stratospheric NO2 during stratospheric warming of January‐February 1979     

M.Q. Syed  A.W. Harrison 《大气与海洋》2013,51(3):216-235

Abstract

Ground‐based measurements of stratospheric NO₂, using absorption spectroscopy of twilight sky in the spectral region 437–451 nm, have been made at Calgary (51.08°N, 114.13°W), Alberta, Canada, during the period December 1978‐March 10, 1979. The NO₂ showed a rather steady behaviour in the month of December when there was no stratospheric warming in progress; the monthly average of the afternoon vertical column abundance for December was 1.7 × 10¹⁵ cm². In the rest of the observation period the NO₂ showed a complex behaviour, but this behaviour appears to be explicable in terms of the stratospheric circulation changes taking place in that period due to the occurrence of a stratospheric warming event.  相似文献   

Experimental constraints on the volatility of germanium,zinc, and lithium in Martian basalts and the role of degassing in alteration of surface minerals     

Alexander Rogaski  Gokce K. Ustunisik  Shuying Yang  Munir Humayun  Kevin Righter  Jeff A. Berger  Nicholas DiFrancesco 《Meteoritics & planetary science》2023,58(9):1183-1210

The surface of Mars is enriched in Cl and S which is linked to volcanic activity and degassing. Similarly, elevated Ge and Zn levels in Gale crater sedimentary bedrock indicate a magmatic source for these elements. To constrain the relative effects of Cl and S on the outgassing of these trace metals and chemical characteristics of primary magmatic vapor deposits incorporated to Martian surface, we conducted a set of degassing and fumarolic alteration experiments. Ge is found to be more volatile than Zn in all experiments. In S-bearing runs, the loss of Ge and Zn was less than any other experiments. In Cl-only runs, degassing of Zn was more than twice that of Ge within the first 10 min and percent loss increased for both elements with increasing time. In Cl + S runs, S-induced reduction of GeO₂ and ZnO to metallic Ge and Zn switches the preference of chloride formation from Zn to Ge. Up to 90% of Ge and Zn loss in the 1-h no volatile-added (NVA) experiments might be due to the small amounts of Cl contamination in NVA mixes via other oxides used for synthesis. Alteration experiments show different phases between 1-h and 24-/72-h runs. In 1-h runs, anhydrite and langbeinite dominate while in 24-/72-h runs halite and sylvite dominate the condensate assemblages. S-bearing phases form as the intermediate products of fumarolic deposition, while chlorides are common when the system is allowed to cool gradually. One-hour exposure was sufficient to form alteration phases and vapor deposits such as NaCl, KCl, CaSO₄, and langbeinites on the Martian analog minerals. These salts were identified in Martian meteorites and in situ measurements. Our results provide evidence that volcanic degassing along with fumarolic alteration could be a potential source for the enrichment and varying abundances of Cl, S, Fe, Zn, Ge in Martian surface, as well as a cause for Ge depletion in shergottites.  相似文献   

Nonlinear analysis of seasonality and stochasticity of the Indus River     

Syed Ahmad Hassan  M. Rashid Kamal Ansari 《水文科学杂志》2013,58(2):250-265

Abstract

One of the world's largest irrigation networks, based on the Indus River system in Pakistan, faces serious scarcity of water in one season and disastrous floods in another. The system is dominated both by monsoon and by snow and glacier dynamics, which confer strong seasonal and inter-annual variability. In this paper two different forecasting methods are utilized to analyse the long-term seasonal behaviour of the Indus River. The study also assesses whether the strong seasonal behaviour is dominated by the presence of low-dimensional nonlinear dynamics, or whether the periodic behaviour is simply immersed in random fluctuations. Forecasts obtained by nonlinear prediction (NLP) and the seasonal autoregressive integrated moving average (SARIMA) methods show that the performance of NLP is relatively better than the SARIMA method. This, along with the low values of the correlation dimension, is indicative of low-dimensional nonlinear behaviour of the hydrological dynamics. A relatively better performance of NLP, using an inverse technique, may also be indicative of the low-dimensional behaviour. Moreover, the embedding dimension of the best NLP forecasts is in good agreement with the estimated correlation dimension. This provides evidence that the nonlinearity inherent in the monthly river flow due to the snowmelt and the monsoon variations dominate over the high-dimensional components and might be exploited for prediction and modelling of the complex hydrological system.

Citation Hassan, S. A. & Ansari, M. R. K. (2010) Nonlinear analysis of seasonality and stochasticity of the Indus River. Hydrol. Sci. J. 55(2), 250–265.  相似文献   

Evolution of stress in Southern California for the past 200 years from coseismic, postseismic and interseismic stress changes   总被引：6，自引：0，他引：6  

Andrew M. Freed  Syed Tabrez Ali  Roland Bürgmann 《Geophysical Journal International》2007,169(3):1164-1179

  相似文献   

Study on mechanochemical effect of silica for short grinding period     

Samayamutthirian Palaniandy  Khairun Azizi Mohd AzizliHashim Hussin  Syed Fuad Saiyid Hashim 《International Journal of Mineral Processing》2007

Silica was ground in an oscillating mill at various grinding period to study the mechanochemical effect in fine grinding process. The ground particles exhibited massive size reduction where the volume moment diameter of 5.56 μm was reached within 600 s. Aggregation of fine particles was very pronounced when it was ground for 600 s due to high surface energy. Aggregation of fine particles caused the ground particles to exhibit poly-modal particle size distribution. Line broadening and reduction of diffractogram peak intensity were observed. Amorphization rate up to 16.9% was exhibited by the particle ground for 600 s. Preferential breakage of plane was observed where (101) and (111) was easily distorted compared to (110) and (200). Rapid reduction of crystallite size was observed at early stage of grinding until it reached a plateau at 5 nm at 600 s whilst the change in lattice strain was 0.5%.  相似文献   

Tungsten and hafnium distribution in calcium-aluminum inclusions (CAIs) from Allende and Efremovka   总被引：1，自引：0，他引：1  

Munir Humayun  Steven B. Simon 《Geochimica et cosmochimica acta》2007,71(18):4609-4627

Recent ¹⁸²Hf-¹⁸²W age determinations on Allende Ca-, Al-rich refractory inclusions (CAIs) and on iron meteorites indicate that CAIs have initial ε¹⁸²W (−3.47 ± 0.20, 2σ) identical to that of magmatic iron meteorites after correction of cosmogenic ¹⁸²W burn-out (−3.47 ± 0.35, 2σ). Either the Allende CAIs were isotopically disturbed or the differentiation of magmatic irons (groups IIAB, IID, IIIAB, and IVB) all occurred <1 m.y. after CAI formation. To assess the extent of isotopic disturbance, we have analyzed the elemental distribution of Hf and W in two CAIs, Ef2 from Efremovka (CV3 reduced), and Golfball from Allende (CV3 oxidized). Fassaite is the sole host of Hf (10-25 ppm) and, therefore, of radiogenic W in CAIs, with ¹⁸⁰Hf/¹⁸⁴W > 10³, which is lowered by the ubiquitous presence of metal inclusions to ¹⁸⁰Hf/¹⁸⁴W > 10 in bulk fassaite. Metal alloy (Ni ∼ 50%) is the sole host of W (∼500 ppm) in Ef2, while opaque assemblages (OAs) and secondary veins are the hosts of W in Golfball. A large metal alloy grain from Ef2, EM2, has ¹⁸⁰Hf/¹⁸⁴W < 0.006. Melilite has both Hf and W below detection limits (<0.01 ppm), but the presence of numerous metallic inclusions or OAs makes melilite a carrier for W, with ¹⁸⁰Hf/¹⁸⁴W < 1 in bulk melilite. Secondary processes had little impact on the ¹⁸²Hf-¹⁸²W systematics of Ef2, but a vein cross-cutting fassaite in Golfball has >100 ppm W with no detectable Pt or S. This vein provides evidence for transport of oxidized W in the CAI. Because of the ubiquitous distribution of OAs, interpretations of the ¹⁸²Hf-¹⁸²W isochron reported for Allende CAIs include: (i) all W in the OAs was derived by alteration of CAI metal, or (ii) at least some of the W in OAs may have been equilibrated with radiogenic W during metamorphism of Allende. Since (ii) cannot be ruled out, new ¹⁸²Hf-¹⁸²W determinations on CAIs from reduced CV3 chondrites are needed to firmly establish the initial W isotopic composition of the solar system.  相似文献   

Re-Os isotopic systematics and platinum group element composition of the Tagish Lake carbonaceous chondrite     

Alan D. Brandon  Munir Humayun  Igor S. Puchtel  Michael E. Zolensky 《Geochimica et cosmochimica acta》2005,69(6):1619-1631

The Tagish Lake meteorite is a primitive C2 chondrite that has undergone aqueous alteration shortly after formation of its parent body. Previous work indicates that if this type of material was part of a late veneer during terrestrial planetary accretion, it could provide a link between atmophile elements such as H, C, N and noble gases, and highly siderophile element replenishment in the bulk silicate portions of terrestrial planets following core formation. The systematic Re-Os isotope and highly siderophile element measurements performed here on five separate fractions indicate that while Tagish Lake has amongst the highest Ru/Ir (1.63 ± 0.08), Pd/Ir (1.19 ± 0.06) and ¹⁸⁷Os/¹⁸⁸Os (0.12564-0.12802) of all carbonaceous chondrites, these characteristics still fall short of those necessary to explain the observed siderophile element systematics of the primitive upper mantles of Earth and Mars. Hence, a direct link between atmophile and highly siderophile elements remains elusive, and other sources for replenishment are required, unless an as yet poorly constrained process fractionated Re/Os, Ru/Ir, and Pd/Ir following late accretion on both the Earth and Mars mantles.The unique elevated Ru/Ir combined with elevated ¹⁸⁷Os/¹⁸⁸Os of Tagish Lake may be attributed to Ru and Re mobility during aqueous alteration very early in its parent body history. The Os, Ir, Pt, and Pd abundances of Tagish Lake are similar to CI chondrites. The elevated Ru/Ir and the higher Re/Os and consequent ¹⁸⁷Os/¹⁸⁸Os in Tagish Lake, are balanced by a lower Ru/Ir and lower Re/Os and ¹⁸⁷Os/¹⁸⁸Os in CM-chondrites, relative to CI chondrites. A model that links Tagish Lake with CI and CM chondrites in the same parent body may explain the observed systematics. In this scenario, CM chondrite material comprises the exterior, grading downward to Tagish Lake material, which grades to CI material in the interior of the parent body. Aqueous alteration intensifies towards the interior with increasing temperature. Ruthenium and Re are mobilized from the CM layer into the Tagish Lake layer. This model may thus provide a potential direct parent body relationship between three separate groups of carbonaceous chondrites.  相似文献   

THE THEME OF "RELEVANCE" IN THIRD WORLD HUMAN SCIENCES     

Syed Farid Alatas 《Singapore journal of tropical geography》1996,16(2):123-140

The fact that the humanities and social sciences in developing societies generally originated in the West has raised the issue of the relevance of these arts and sciences to the needs and problems of Third World societies. This questioning of relevance has led, in turn, to the call for the indigenisation of knowledge in developing societies. While there has been a great deal of discussion on indigenisation, there has been little practice of indigenised humanities and social science. As a result, there are few examples of what indigenous knowledge constitutes from theoretical, methodological and empirical points of view. This paper is directed towards arriving at some conception of what indigenised knowledge is, the various forms that it takes, and its rationale.  相似文献   

Highly siderophile elements in ureilites     

K. Rankenburg  M. Humayun  J.S. Herrin 《Geochimica et cosmochimica acta》2008,72(18):4642-4659

The abundances of the highly siderophile elements (HSE) Ru, Pd, Re, Os, Ir, and Pt were determined by isotope dilution mass spectrometry for 22 ureilite bulk rock samples, including monomict, augite-bearing, and polymict lithologies. This report adds significantly to the quantity of available Pt and Pd abundances in ureilites, as these elements were rarely determined in previous neutron activation studies. The CI-normalized HSE abundance patterns of all ureilites analyzed here except ALHA 81101 show marked depletions in the more volatile Pd, with CI chondrite-normalized Pd/Os ratios (excluding ALHA 81101) averaging 0.19 ± 0.23 (2σ). This value is too low to be directly derived from any known chondrite group. Instead, the HSE bulk rock abundances and HSE interelement ratios in ureilites can be understood as physical mixtures of two end member compositions. One component, best represented by sample ALHA 78019, is characterized by superchondritic abundances of refractory HSE (RHSE—Ru, Re, Os, Ir, and Pt), but subchondritic Pd/RHSE, and is consistent with residual metal after extraction of a S-bearing metallic partial melt from carbonaceous chondrite-like precursor materials. The other component, best represented by sample ALHA 81101, is RHSE-poor and has HSE abundances in chondritic proportions. The genesis of the second component is unclear. It could represent regions within the ureilite parent body (UPB), in which metallic phases were completely molten and partially drained, or it might represent chondritic contamination that was added during disruption and brecciation of the UPB. Removal of carbon-rich melts does not seem to play an important role in ureilite petrogenesis. Removal of such melts would quickly deplete the ureilite precursors in Re/Os and As/Au, which is inconsistent with measured osmium isotope abundances, and also with literature As/Au data for the ureilites. Removal of ²⁶Al during silicate melting may have acted as a switch that turned off further metal extraction from ureilite source regions.  相似文献   

Groundwater control for construction purposes: a case study from Kuwait   总被引：1，自引：0，他引：1  

Fathi M. Shaqour  Syed E. Hasan 《Environmental Geology》2008,53(8):1603-1612

One of the major rehabilitation projects in Kuwait during the 1990s was improvement of the wastewater treatment plant at Jahra, a town 30 km north of Kuwait City. The project incorporates construction of a pumping station to collect the sewage via a network of sewer lines throughout the city. Groundwater occurs 4 m below the ground surface and construction specifications required lowering the groundwater table by 16 m to the foundation grade, 20 m below the ground surface. Open excavation with four stage well point system of dewatering was selected to ensure dry foundation conditions; but the system failed to lower the groundwater table down to the desired depth. Review of site investigation records and recalculation of field hydraulic conductivity resulted in design changes, augmenting the well point system with a number of deep wells and sumps to lower the water table down to the foundation grade. The paper discusses subsurface conditions and presents an analysis of the cause of failure of the well point system. The actual hydraulic conductivity proved to be several folds higher than the calculated one that was determined using Hazen’s formula. It was found that use of Hazen’s formula led to serious underestimation of field hydraulic conductivity. It is advised not to use such formulas without thorough investigation and proper interpretation of borehole data.  相似文献