Self-interacting dark matter from the hidden heterotic-string sector

It has been suggested recently that self-interacting dark matter (SIDM) fits better the observational characteristics of galaxy dynamics. We propose that the SIDM is composed from the glueballs of the hidden sector non-Abelian gauge group, while the hidden matter states exist in vector-like representation and decouple from the light spectrum. It is shown that these glueballs are semi-stable with the lifetime larger than the present age of the Universe, if their mass is 1 GeV or less. The constraint on their abundance today suggests that the energy was stored in the hidden sector soon after inflation. This imposes an upper limit on the reheating temperature. We further study the naturalness of this scenario in the context of the free-fermionic string models and point out a class of such models where the SIDM from the hidden sector is indeed plausible.     

The mechanism of Lake Kinneret salinization as a linear reservoir

The salinity of Lake Kinneret, Israel, is significantly higher than the salinity of the water from surface streams that flow to the lake. The relatively high salinity is a result of the activity of saline springs located at the bottom of the lake.The purpose of this work is to establish a general model for the salinization mechanism of Lake Kinneret. The model is based on the main components of the annual water and solute balance. Changes in time of the solute mass of the lake were described as a differential equation of a linear reservoir on an annual time scale. The model assumes that under any long-term operation policy of the lake, the components of the annual solute and water balance stay nearly constant in time.The model was tested for both steady-state conditions, and during changes in time, against measured lake salinity over the years 1968-2000. It was found that the major changes of lake salinity throughout the years were described well, despite the variety of rainfall amounts. Predictions of the expected lake salinity changes were proposed for the cases of controlled increase or decrease of saline springs discharge to the lake; for the changes of water quantity allowed to flow into or pumped out of the lake; and for various initial salinities. Predictions agree well with previous predictions made by statistical models.     

Effect of nitrogen amendments on microbial biomass, above-ground biomass and nematode population in the Negev Desert soil

Nitrogen amendments (0, 25, 50 and 100 kg NH₄NO₃/ha) were used to study the responses of primary production, microbial biomass and nematode population in desert soil. The study was conducted in the Israeli Negev Desert, a region characterized by low and randomly distributed rainfall. Over a 1-year study period, nitrogen amendments resulted in a significant (p<0·01) increase in soil microbial biomass. Soil microbial biomass also increased concomitantly with the increase in soil organic matter. The number of free-living nematodes in the soil increased with the increase in soil moisture, ranging from 43,000 individuals per square metre at the end of the summer to 351,000 individuals per square metre during the rainy season. No significant correlation was found between the nitrogen treatments and the nematode population, whereas a significant positive correlation was found between the nitrogen amendments and the above-ground biomass (r²=0·94, p<0·03). The nitrate proportion of the total soluble nitrogen in the soil also increased with the increase in soil moisture. This study provides baseline data for nitrogen amendments on soil microbial status, as well as insights into the importance of nitrogen in fertility in arid environments.     

Effect of extreme rainfall events on the water resources of the Jordan River

As a response to climate change, shifting rainfall trends including increased multi-year droughts and an escalation in extreme rainfall events are expected in the Middle East. The purpose of this study is to evaluate the potential impact of these shifting trends on stream flow in the Jordan River and its tributaries. We use a non-homogeneous hidden Markov model to generate artificial daily rainfall simulations which capture independently shifting trends of increased droughts and escalated extreme. These simulations are then used as input into a hydrological model calibrated for the upper catchments of the Jordan River to compare the impact on stream flow and water resources between the different rainfall scenarios. We compare the predicted baseflow and surface flow components of the tested watersheds, and find that while an increase in extreme rainfall events increases the intensity and frequency of surface flow, the over all flow to the Jordan River, and the characteristics of the baseflow in the Jordan River system is not largely impacted. In addition, though it has been suggested that in the case of a multi-year drought the karstic nature of the aquifer might lead to more intense, non-linear reductions in stream flow, here we quantify and show the conditions when annual stream flow reduce linearly with rainfall, and when these relations will become non-linear.     

The role of labile sulfur compounds in thermochemical sulfate reduction

The reduction of sulfate to sulfide coupled with the oxidation of hydrocarbons to carbon dioxide, commonly referred to as thermochemical sulfate reduction (TSR), is an important abiotic alteration process that most commonly occurs in hot carbonate petroleum reservoirs. In the present study we focus on the role that organic labile sulfur compounds play in increasing the rate of TSR. A series of gold-tube hydrous pyrolysis experiments were conducted with n-octane and CaSO₄ in the presence of reduced sulfur (e.g. H₂S, S°, organic S) at temperatures of 330 and 356 °C under a constant confining pressure. The in-situ pH was buffered to 3.5 (∼6.3 at room temperature) with talc and silica. For comparison, three types of oil with different total S and labile S contents were reacted under similar conditions. The results show that the initial presence of organic or inorganic sulfur compounds increases the rate of TSR. However, organic sulfur compounds, such as 1-pentanethiol or diethyldisulfide, were significantly more effective in increasing the rate of TSR than H₂S or elemental sulfur (on a mole S basis). The increase in rate is achieved at relatively low concentrations of 1-pentanethiol, less than 1 wt% of the total n-octane, which is comparable to the concentration of organic S that is common in many oils (∼0.3 wt%). We examined several potential reaction mechanisms to explain the observed reactivity of organic LSC. First, the release of H₂S from the thermal degradation of thiols was discounted as an important mechanism due to the significantly greater reactivity of thiol compared to an equivalent amount of H₂S. Second, we considered the generation of olefines in association with the elimination of H₂S during thermal degradation of thiols because olefines are much more reactive than n-alkanes during TSR. In our experiments, olefines increased the rate of TSR, but were less effective than 1-pentanethiol and other organic LSC. Third, the thermal decomposition of organic LSC creates free-radicals that in turn might initiate a radical chain-reaction that creates more reactive species. Experiments involving radical initiators, such as diethyldisulfide and benzyldisulfide, did not show an increase in reactivity compared to 1-pentanethiol. Therefore, we conclude that none of these can sufficiently explain our observations of the initial stages of TSR; they may, however, be important in the later stages. In order to gain greater insight into the potential mechanism for the observed reactivity of these organic sulfur compounds during TSR, we applied density functional theory-based molecular modeling techniques to our system. The results of these calculations indicate that 1-pentanethiol or its thermal degradation products may directly react with sulfate and reduce the activation energy required to rupture the first S-O bond through the formation of a sulfate ester. This study demonstrates the importance of labile sulfur compounds in reducing the onset timing and temperature of TSR. It is therefore essential that labile sulfur concentrations are taken into consideration when trying to make accurate predictions of TSR kinetics and the potential for H₂S accumulation in petroleum reservoirs.     

Influence of land use on the quality of runoff along Israel′s coastal strip (demonstrated in the cities of Herzliya and Ra′anana)

This study presents an analysis of the quality of urban runoff from various land uses by remote‐sensing and GIS technology coupled with hydrological and chemical monitoring. The study areas were located in the cities of Herzliya and Ra′anana, in Israel′s coastal plain, where extensive urbanization has occurred over the last 30 years. Land uses in urban basins were analysed; rain and runoff were measured and sampled at measurement stations representing different land uses (residential, industrial, commercial and roads). The aim was to analyse uses by different remote‐sensing and GIS techniques, to evaluate the quality of urban storm water from various land uses and to verify a method for predicting the impact of urban land uses on the quantity and quality of urban storm water. The quality of urban storm water from residential areas was generally very high, and the water is suitable for reuse or direct recharge into the local aquifer. In light of the serious state of the Israeli water sector and the large amounts of unused runoff produced by Israel′s cities, together with the high quality of urban storm water drained from the residential areas, it is important to exploit this water source. Copyright © 2014 John Wiley & Sons, Ltd.     

Seasonal variability of soil phosphate stable oxygen isotopes in rainfall manipulation experiments

Phosphorus (P) availability limits productivity in many ecosystems worldwide. As a result, improved understanding of P cycling through soil and plants is much desirable. The use of the oxygen isotopes associated to phosphate can be used to study the cycle of P in terrestrial systems. However, changes with time in the oxygen isotopes associated to available P have not yet been evaluated under field conditions. Here we present the variations in available-P oxygen isotopes, based on resin extractions, in a semi-arid site that included plots in which the amount of rainfall reaching the soil was modified. In addition, the oxygen isotopes in the less dynamic fraction which is extractable by HCl, were also measured. The δ¹⁸O of the HCl-extractable phosphate shows no seasonal pattern and corresponds to the average value of the available phosphate of 16.5‰. This value is in the expected range for equilibration with soil water at the prevailing temperatures in the site. The δ¹⁸O values of resin-extractable P showed a range of 14.5-19.1‰ (SMOW), and evidence of seasonal variability, as well as variability induced by rainfall manipulation experiments. We present a framework for analyzing the isotopic ratios in soil phosphate and explain the variability as mainly driven by phosphate equilibration with soil water, and by the isotopic effects associated with extracellular mineralization. Additional isotopic effects result from fractionation in uptake, and the input to the soil of phosphate equilibrated in leaves. These results suggest that the δ¹⁸O of resin-extractable P is an interesting marker for the rate of biological P transformations in soil systems.