Storm-generated,hummocky stratification on the outer-Scotian Shelf     

Carl L. Amos  M. Z. Li  K. -S. Choung 《Geo-Marine Letters》1996,16(2):85-94

Hummocky megaripples occur on Sable Island Bank, Scotian Shelf. Submersible observations show that the megaripples form during winter storms and are subsequently obliterated through bioturbation and fair-weather reworking. The megaripples of this study were underlain by a storm bed composed of: (A) a basal scoured and infilled gravel lag facies; (B) low-angle tangential crossbedding in gravel to coarse sand; (C) anisotropic hummocky stratification in medium sand; and (D) wave ripple cross-lamination in medium/fine sand. This sequence forms a tempestite bed created by a winter storm during our sampling program. Numerical simulation of bed conditions during the storm suggests that the hummocky megaripples and hummocky stratification formed together during late stages of storm decay from conditions of sheet flow. Near-bed wave motion during deposition exceeded steady currents by an order of magnitude.  相似文献   

Low-mass red giants and masses of NPNs     

Amos Harpaz  Giora Shaviv 《Astrophysics and Space Science》1992,189(1):11-21

The evolutionary track of low-mass red giant stars (0.7–0.9M ) is computed with the aim to demonstrate the conditions under which low-mass white dwarfs (WDs) can form through the evolution of single stars. Also, the influence of the mixing length to the scale height ratio on the radius of the star is calculated and the coupling between the mixing-length and the mass-loss rate parameters is investigated. Our conclusions are that the uncertainties in mass-loss and mixing-length to scale-height ratio leave enough parameter space to allow the formation of low-mass WD via single star evolution. We also conclude that the gap between proto-WD stars without any nebula and stars with well-defined nebulae is bridged by stars which have a dilute gas cloud around them which cannot be observed as a nebula.  相似文献   

Assessing factors affecting drought,earthquake, and flood risk perception: empirical evidence from Bangladesh     

Mallick  Javed  Salam  Roquia  Amin  Ruhul  Islam  Abu Reza Md. Towfiqul  Islam  Aznarul  Siddik  Md. Nur Alam  Alam  G. M. Monirul 《Natural Hazards》2022,112(2):1633-1656

Natural Hazards - Understanding household disaster risk perception is crucial to formulate and apply disaster risk reduction strategies. Using survey data from 300 households from three highly...  相似文献   

A model of sand transport in Treporti channel: northern Venice lagoon     

Georg Umgiesser  Francesca De Pascalis  Christian Ferrarin  Carl L. Amos 《Ocean Dynamics》2006,56(3-4):339-351

The origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 μm, one outlier of 300 μm was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation.  相似文献   

The role of ballast in the helium-shell flash     

Amos Harpaz 《Monthly notices of the Royal Astronomical Society》2010,401(1):242-244

Calculations are presented of the evolutionary track of an asymptotic giant branch (AGB) star, after most of its envelope is consumed and it starts moving to the right in the Hertzsprung–Russell (HR) diagram. On looking for the conditions that may create a helium-shell flash at this stage, it is found that a necessary condition for the creation of a helium-shell flash at this stage is the presence of mass 'ballast' over the helium-burning shell. The effects of different amounts of such ballast are studied, and the detailed evolution of such a flash is presented.  相似文献   

Warming of an elevated layer over the Caribbean     

Mark R. Jury  Amos Winter 《Climatic change》2010,99(1-2):247-259

Air temperatures in the trade wind inversion (~850 hPa) over the Caribbean have been rising much faster than sea temperatures. This is associated with an accelerated Hadley circulation, with sinking motions over the Caribbean corresponding with increasing rising motion over the Amazon. The sinking motions induce a faster rate of warming and drying in the trade wind inversion than at other levels. Much of the trend in Caribbean climate is attributable to physical mechanisms; changes in atmospheric composition play a secondary role. Smoke and dust plumes from Africa, drifting westward across the Atlantic, enhance the greenhouse effect in an elevated (1–3 km) layer. A stabilized lower atmosphere across the Caribbean has contributed to warming and drying trends over the twentieth century which are projected to continue. The atmosphere is warming faster than the ocean, causing a decline in sensible heat fluxes that fuel tropical cyclones.  相似文献   

Volcanic gaps due to oblique consumption of aseismic ridges   总被引：1，自引：0，他引：1  

Amos Nur  Zvi Ben-Avraham 《Tectonophysics》1983,99(2-4)

The present-day consumption of oceanic ridges and other buoyant rises and fragments at circum-Pacific subduction zones, and presumably elsewhere, are closely related to existing gaps in volcanism. Examples are the gaps associated with the Nazca, Juan Fernandez, Cocos, Marcus-Necker and Louisville ridges. The buoyancy of these ridges breaks the continuity of the subducted plate, which may lead to reduced water supply required for melting of magma, and therefore create temporary volcanic gaps. The oblique consumption of these ridges causes the gap to migrate with time. This mechanism may be useful in interpreting time-space patterns of past volcanic chains associated with subduction in terms of the consumption of the disruptive oceanic plateaus and ridges.  相似文献   

Thermodynamic properties,low-temperature heat-capacity anomalies,and single-crystal X-ray refinement of hydronium jarosite, (H<Subscript>3</Subscript>O)Fe<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>6</Subscript>     

J.?MajzlanEmail author  R.?Stevens  J.?Boerio-Goates  B. F.?Woodfield  A.?Navrotsky  P. C.?Burns  M. K.?Crawford  T. G.?Amos 《Physics and Chemistry of Minerals》2004,31(8):518-531

Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO₄ solutions. Single-crystal XRD refinement with R₁=0.0232 for the unique observed reflections (|F_o| > 4_F) and wR₂=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, V^o=160.11(4) cm³, and fractional positions for all atoms except the H in the H₃O groups. The chemical composition of this sample is described by the formula (H₃O)_0.91Fe_2.91(SO₄)₂[(OH)_5.64(H₂O)_0.18]. The enthalpy of formation (H^o_f) is –3694.5 ± 4.6 kJ mol^–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H₂O, and -MgSO₄. The entropy at standard temperature and pressure (S^o) is 438.9±0.7 J mol^–1 K^–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (C_p) data between 273 and 400 K were fitted to a Maier-Kelley polynomial C_p(T in K)=280.6 + 0.6149T–3199700T^–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol^–1. Speciation and activity calculations for Fe(III)–SO₄ solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the C_p data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in C_p, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H₃O)Fe₃(SO₄)₂(OH)₆ was estimated: G^o_f= –3226.4 ± 4.6 kJ mol^–1, H^o_f=–3770.2 ± 4.6 kJ mol^–1, S^o=448.2 ± 0.7 J mol^–1 K^–1, C_p (T in K)=287.2 + 0.6281T–3286000T^–2 (between 273 and 400 K).  相似文献   

The rupture process during the 1999 Düzce, Turkey, earthquake from joint inversion of teleseismic and strong-motion data     

Nur Umutlu  Kazuki Koketsu  Claus Milkereit 《Tectonophysics》2004,391(1-4):315

Teleseismic and strong-motion data are inverted to determine the rupture process during the November 1999 Düzce earthquake in NW Turkey. The fault geometry, rise time and rupture velocity are determined from the aftershock distribution and preliminary inversions of the teleseismic data. Joint inversion of the teleseismic and strong-motion data is then carried out for the slip distribution. We obtain the strike 264°, dip 64°, rake −172°, seismic moment 5.0×10¹⁹ N m (M_w 7.1), and average stress drop 7 MPa. This earthquake was characterized by bilateral fault rupture and asymmetric slip distribution. Two asperities (areas of large slip) are identified, the eastern one being 1.5 times larger than the western one. The derived slip distribution is consistent with the aftershock distribution, surface rupture and damage. The point of rupture initiation in this Düzce earthquake coincided with the eastern tip of the aftershock distribution of the August 1999 Izmit earthquake.  相似文献   

Salt cave cross-sections and their paleoenvironmental implications     

Amos Frumkin 《Geomorphology》1998,23(2-4)

Salt caves respond rapidly to environmental changes. Direct measurement and ¹⁴C dating show that complex cross-sections may develop in a few hundred years. Two basic forms are discussed: (1) ingrowing vadose canyons where changing width may correspond to changing discharge; (2) wide low passages with flat ceilings, developed by upward dissolution, which may indicate rising base level. Some cross-sections are deformed by Holocene tectonics.  相似文献