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1.
Nir J. Shaviv 《Astrophysics and Space Science》1995,231(1-2):445-448
The temporal behavior of GRBs is quantified using a power spectrum analysis. The power spectrum of great variety of GRBs is well represented by the simple
–2 behavior. We then study a cosmological GRB model in which relativistic flows interact with dense radiation fields. This mechanism in the densest stellar regions known to exist, surprisingly yields the correct temporal behavior. Other characteristics are also reproduced, including the duration bimodality and the hardness-duration distribution. 相似文献
2.
A. Nir 《Journal of Hydrology》1973,19(1):33-41
Tracer concentration in mixed lakes was usually calculated under assumption of steady hydrologic state, i.e., constant input, output, and volume. Departures from steady state were treated by the use of average flow or weighting the concentration by inflow values. An exact analytical solution indicates the limits of validity of the above approximations. The exact solution can be adapted for multiple inputs and outputs, exchange with atmospheric moisture, evaporation with isotope fractionation and formation of epilimnion. The solution is simplified for certain types of connection between outflow and volume. 相似文献
3.
Nir Cohen 《GeoJournal》2007,68(2-3):267-278
This paper deploys a critical discourse analysis methodology to examine the emergence of three (sometimes overlapping) discourses on emigration in Israel. It examines the linkages between the various discursive phases and processes of (trans-) national identity formation among emigrants. It argues that emigration discourses have often been strong predictors of subsequent changes in state policies—and other programmatic initiatives—aimed at Israeli citizens abroad. By juxtaposing the discursive construction of emigration (and its linkages to nation-forming political strategies in Israel) and the effects they have had on emigrant identities the paper contributes to the emerging literature on state-diaspora relations and transnational politics. 相似文献
4.
The 18O/16O ratio of CO2 is a potentially powerful tracer of carbon dioxide fluxes from the soil to the atmosphere, which is influenced by complex interactions involving both biotic and abiotic soil processes. We use a simplified experimental approach and numerical simulations to examine in isolation the 18O exchange between CO2 and soil water associated with the abiotic invasion of atmospheric CO2 into soil. This allowed us to verify, in particular, whether the 18O of the retro-diffusion flux of CO2 from the soil reflects 18O equilibration with water at the soil surface, or at some depth. Sterile soil samples with known water isotopic composition were placed in a closed box attached to a specially designed flow chamber and the changes in δ18O of CO2 between the chamber inlet and outlet, due only to invasion effects, were determined. Numerical simulations constrained by the laboratory gas exchange measurements indicated that between the two commonly used diffusion models [Penman, H.L. (1940). Gas and vapor movements in soil, 1: the diffusion of vapors through porous solids. Int. J. Agric. Sci.30, 437-462; Moldrup, P., Olesen, T., Yamaguchi, T., Schjonning, P., Rolston, D.E. (1999). Modeling diffusion and reaction in soils, IX, the Backingham-Burdine-Campbell equation for gas diffusivity in undisturbed soil. Soil Sci.164, 542-551], only the former provided good agreement with the measurements over a wide range of soil water contents. Based on the model calculations constrained by experimental data, and on comparison of characteristic diffusion/reaction times, we conclude that the depth required for full CO2-water 18O equilibration ranges between 2 and 8.5 cm. The depth depends, in order of importance, on (1) soil moisture content; (2) temperature, which dominates the rate of hydration isotopic exchange; (3) CO2 residence time, which is determined by the time of replacement of the column air above the soil; and (4) soil structure, including porosity, tortuosity and grain size, with the later probably influencing the water surface area exposed to CO2 exchange. Using field data from a semi-arid forest site in Israel, numerical simulations indicated that the 18O full equilibrium depth varied at this site between 4 cm (January) and 8 cm (November), being sensitive mostly to temperature and soil water content. Deepening of the equilibration depth as the soil dries should limit the effects of 18O evaporative enrichment at the surface on the isotopic composition of the soil-atmosphere CO2 flux. 相似文献
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6.
Blazar emission of gamma rays and cosmic ray production of gamma rays in gas-rich clusters have been proposed recently as alternative sources of the high energy extragalactic diffuse gamma ray background radiation. We show that these sources also produce very different high energy extragalactic diffuse neutrino background radiations. An extragalactic neutrino background radiation may be detected by the new generation of large neutrino telescopes under construction and may be used to trace the origin of the extragalactic gamma radiation. 相似文献
7.
Decadal prediction using climate models faces long-standing challenges. While global climate models may reproduce long-term shifts in climate due to external forcing, in the near term, they often fail to accurately simulate interannual climate variability, as well as seasonal variability, wet and dry spells, and persistence, which are essential for water resources management. We developed a new climate-informed K-nearest neighbour (K-NN)-based stochastic modelling approach to capture the long-term trend and variability while replicating intra-annual statistics. The climate-informed K-NN stochastic model utilizes historical data along with climate state information to provide improved simulations of weather for near-term regional projections. Daily precipitation and temperature simulations are based on analogue weather days that belong to years similar to the current year's climate state. The climate-informed K-NN stochastic model is tested using 53 weather stations in the Northeast United States with an evident monotonic trend in annual precipitation. The model is also compared to the original K-NN weather generator and ISIMIP-2b GFDL general circulation model bias-corrected output in a cross-validation mode. Results indicate that the climate-informed K-NN model provides improved simulations for dry and wet regimes, and better uncertainty bounds for annual average precipitation. The model also replicates the within-year rainfall statistics. For the 1961–1970 dry regime, the model captures annual average precipitation and the intra-annual coefficient of variation. For the 2005–2014 wet regime, the model replicates the monotonic trend and daily persistence in precipitation. These improved modelled precipitation time series can be used for accurately simulating near-term streamflow, which in turn can be used for short-term water resources planning and management. 相似文献
8.
Yaacov Arkin 《Environmental Geology》1988,11(1):5-14
Disintegration of marl slopes in Israel is directly related to the climatic characteristics of the region even where water
is not an obvious component of the environment. Seasonal contrasts between long, dry summers and short, wet winters are manifested
by wide ranges in temperature (13–26°C) and water content (5−>42 percent) within the marl. These variations lead to both solution
and aggregation of carbonate material in the marl.
Chemical disintegration in summer followed by mechanical disintegration in winter causes progressive weakening of the marl.
The repeated wetting and drying results in the formation of an open texture in the marl.
Scanning electron microscope (SEM) observations made over several seasons on marl from freshly excavated slopes confirm the
progressive disintegration from the slope's surface to a depth of at least 1.50 m. Solution holes, channels, and gaps between
aggregates and matrix, formed during the summer, greatly increase the effective porosity and permeability of the marl. Water
infiltration in the winter results in the mechanical washing out of fine material to the surface of the slope by throughflow
and piping. 相似文献
9.
Mesbahzadeh Tayyebeh Salajeghe Ali Sardoo Farshad Soleimani Zehtabian Gholamreza Ranjbar Abbas Krakauer Nir Y. Miglietta Mario Marcello Mirakbari Maryam 《Natural Hazards》2020,104(2):1801-1817
Natural Hazards - Dust storms are a major natural hazard to human health. Severe erosive storms in parts of the Central Plateau of Iran have made the situation very difficult for the inhabitants,... 相似文献
10.
Irrigation induced surface cooling in the context of modern and increased greenhouse gas forcing 总被引：1，自引：0，他引：1
There is evidence that expected warming trends from increased greenhouse gas (GHG) forcing have been locally ??masked?? by irrigation induced cooling, and it is uncertain how the magnitude of this irrigation masking effect will change in the future. Using an irrigation dataset integrated into a global general circulation model, we investigate the equilibrium magnitude of irrigation induced cooling under modern (Year 2000) and increased (A1B Scenario, Year 2050) GHG forcing, using modern irrigation rates in both scenarios. For the modern scenario, the cooling is largest over North America, India, the Middle East, and East Asia. Under increased GHG forcing, this cooling effect largely disappears over North America, remains relatively unchanged over India, and intensifies over parts of China and the Middle East. For North America, irrigation significantly increases precipitation under modern GHG forcing; this precipitation enhancement largely disappears under A1B forcing, reducing total latent heat fluxes and the overall irrigation cooling effect. Over India, irrigation rates are high enough to keep pace with increased evaporative demand from the increased GHG forcing and the magnitude of the cooling is maintained. Over China, GHG forcing reduces precipitation and shifts the region to a drier evaporative regime, leading to a relatively increased impact of additional water from irrigation on the surface energy balance. Irrigation enhances precipitation in the Middle East under increased GHG forcing, increasing total latent heat fluxes and enhancing the irrigation cooling effect. Ultimately, the extent to which irrigation will continue to compensate for the warming from increased GHG forcing will primarily depend on changes in the background evaporative regime, secondary irrigation effects (e.g. clouds, precipitation), and the ability of societies to maintain (or increase) current irrigation rates. 相似文献