University of Jordan

About: University of Jordan is a education organization based out in Amman, Jordan. It is known for research contribution in the topics: Population & Medicine. The organization has 7796 authors who have published 13764 publications receiving 213526 citations.

Particulate matter filtration and seasonal nutrient dynamics in permeable carbonate and silicate sands of the Gulf of Aqaba, Red Sea

Abstract: This study compares mineralization in permeable silicate and carbonate sands in the shallow shelf of the Gulf of Aqaba. From July 1999 to March 2000, we monitored concentrations of inorganic nutrients in water and pore water at two neighboring sites, one dominated by silicate, the other by carbonate sand. Although the carbonate was coarser than the quartz sand, organic matter, dissolved inorganic nitrogen (DIN), and ortho-phosphate concentrations in the biogenic carbonate sediment always exceeded those in the terrigenic silicate sands (factor 1.5–2.0 for organic matter, 1.7–14.0 for nutrients). Higher nutrient concentrations in the water column during winter months caused increases in pore-water nutrient concentrations in both sediments down to 10 cm depth with no significant delay, emphasizing the effect of advective transport of solutes and particles into permeable sands. An experiment was conducted where sieved clean quartz and carbonate sands of same grain size (250–500 µm) were incubated in-situ. Although exposed to the same water and boundary current conditions, the sieved carbonate sand accumulated more organic matter and developed higher nutrient concentrations than the incubated silicate sediment. We conclude that the mineralogical characteristics of the carbonate sand (higher porosity, sorption capacity and pH buffer capacity) enhance the filtration capacity, and the biocatalytic conversion efficiency relative to the smooth crystalline quartz grains.

Analytical Study of Fractional-Order Multiple Chaotic FitzHugh-Nagumo Neurons Model Using Multistep Generalized Differential Transform Method

Abstract: The multistep generalized differential transform method is applied to solve the fractional-order multiple chaotic FitzHugh-Nagumo (FHN) neurons model The algorithm is illustrated by studying the dynamics of three coupled chaotic FHN neurons equations with different gap junctions under external electrical stimulation The fractional derivatives are described in the Caputo sense Furthermore, we present figurative comparisons between the proposed scheme and the classical fourth-order Runge-Kutta method to demonstrate the accuracy and applicability of this method The graphical results reveal that only few terms are required to deduce the approximate solutions which are found to be accurate and efficient

Optimal use of irrigation water in the Jordan Valley : A case study

Abstract: Water shortage is a serious problem in most countries in theMiddle East. Irrigation water consumes about three-fourths of theavailable fresh water resources in Jordam and many othercountries in the region. This article presents a practical approachto manage and optimize the irrigation water use in the region.The ultimate objective is to minimize the outside water and tomanage the irrigation water use under geographic,socio-economic, and demographic constraints. This approach usesthe added value (net revenue) of one cubic meter of waterconcept in evaluating different irrigation water use management.This concept has been demonstrated, based on a case study in theJordan Valley.This case study shows that water scarcity can be incorporated inirrigation water management by proper choice of crops andfarming patters. The objective function is to maximize the netrevenue from the agricultural production process subjected tolimitation on water and other production and marketing factors.Results of analysis showed that a net water saving of about9%occurred if the objective function is to minimize water useunder the same level of profitability. This example shall beuseful for water and agricultural planners. Sometimes virtualwater is widely exported in form of crops that consumes largeamounts of water without full economic consideration to theadded value of water. In some cases, food imports may be afeasible option in water-poor countries instead of water import.

Evolutionary substitutions and the antigenic structure of globular proteins.

Abstract: A FEW years ago, Crumpton1 and Reichlin2 reviewed information about the antigenic structure of globular proteins of known amino acid sequence and three-dimensional structure. It seemed that only a small fraction of the amino acid residues in such proteins participated directly in antibody binding. This impression was reinforced by Atassi and co-workers, who proposed antigenic structures of two such proteins—sperm whale myoglobin3 and chicken lysozyme c (ref.4). These workers claim to have identified all those amino acid residues which bind to antibodies present in antisera directed against the protein. These claims stem from extensive studies with chemically modified forms of the protein as well as with antigenically active fragments obtained by specific cleavage of the protein. The antigenic residues are arranged in groups called determinants, each of which binds a specific class of antibodies. A typical determinant contains four to seven residues. For both lysozyme and myoglobin, the proportion of antigenic residues is about 15% of the total number of amino acid residues in the protein3,4. Information has also accumulated concerning the power of antisera to detect evolutionary substitutions of amino acids in globular proteins. Quantitative immunological comparisons of related proteins of known amino acid sequence have consistently shown a strong correlation between degree of sequence difference and degree of antigenic difference. This has been demonstrated most thoroughly for monomeric globular proteins such as lysozymes5,6, ribonucleases7, azurins8 and cytochromes c (refs 9, 10). Less complete information suggests that the correlation holds also for plastocyanins10, tryptophan synthetase α subunits11, serum albumins12, carbonic anhydrases and myoglobins13 (A. B. Champion, E. M. Prager, S. L. Welch, and A. C. Wilson, unpublished), and ferredoxins14. From the strength of the correlations observed for lysozymes, ribonucleases, azurins and cytochromes (r > 0.9), one may make the statistical inference that about 80% (that is, 0.9 squared) of those amino acid substitutions which accumulate during evolution are immunologically detectable7. Here we summarise additional evidence that the majority of evolutionary substitutions are immunologically detectable, and we discuss how to reconcile this evidence with the chemical evidence that only a small fraction of the amino acids are antigenic.