15N-labelled urea recovery by different crops in the Sudan Gezira soil

The aim of this work was to provide practical information on the efficient utilization of urea-nitrogen by wheat, cotton and sorghum using¹⁵N isotopic tracer method. The utilization efficiency of applied nitrogen was found to be dependent on the crop ability to remove nitrogen from the soil solution over a relatively short period. Mixing 42 kg P per ha with 84 kg N increased wheat grain yield by about 30%, and N recovery by about 50% over the same N treatment without P. Placement of urea 10–20 cm deep increased %Ndff by cotton over surface-application by about 45% and the % N recovery by about 55%. N recovery by sorghum was low, and was improved slightly by application of urea four weeks after sowing compared to application at sowing. Loss of N as NH₃ from surface applied urea was presumably the major avenue of loss which reduced N recovery by the different crops, especially sorghum and cotton. Urea-N recoveries calculated by the difference method and the¹⁵N isotopic method show the more reliability of the latter method.     

Effects of Operator Stance on Pushing and Pulling Tasks

A considerable amount of research has been done to determine the magnitudes of forces man can exert on loads. However, very little has been done to determine the optimum configurations an operator should assume in front of a load to be most effective. This paper presents the methodology and results of an investigation concerning these skeletal configurations and selects an optimum for pushing as well as pulling of loads. In addition, a biomechanical analysis of the forces and torques developed at various joints is included.     

Systems aspects of large scale nuclear science programming

The first reported extraction of the detailed collision matrix for a nuclear interaction - for the specific case of protons on ²⁰⁶Pb - is here presented as an effective illustration of the complex interweaving of principles of organization with principles of scientific computer programming. Methodology is presented for the integration of new and distinctive computer technological developments into the scientific programming function.     

The Lipids of Schistosomes During their Various Stages of Growth

Presence of appreciable amount of squalene in the intermediate stages of both species of schistosomes was detected. Squalene was found to be absent in adult S. mansoni worm. The major components of the developmental stages of schistosomes were assessed as well. Chromatographic separation of lipid classes of the livers of biomphalaria snails, both infected with S. mansoni and uninfected was also carried out.     

Curing Behavior of Epoxy Resin Using Controllable Curing Agents Based on Nickel Complexes

Summary: The curing reaction kinetics and mechanism of the diglycidyl ether of bisphenol A (DGEBA) with three complexes of Ni(II) with diethylentriamine (Dien), Pyrazole (Pz) and Pyridine (Py) as ligands have been studied using differential scanning calorimetry (DSC). The curing reaction was characterized by high cure onset and peak maximum temperatures. The kinetics of the curing reaction were evaluated using the Ozawa method. The average values of activation energy for the three nickel complexes increased in the order: Dien‐based curing agent > Pz‐based curing agent > Py‐based curing agent. Three main curing mechanisms (catalytic, complex cation and free ligand polymerization path) have been proposed depending on the cure temperature. It was also shown that the cure kinetics of DGEBA with Dien‐ and Py‐based complexes could be described by the Sestak‐Berggren equation. The water absorption, chemical resistance and thermal stability of the thermosets were also studied. The results showed that the thermoset obtained with the Py‐based complex was more thermally stable than those obtained with the other two curing agents.

Activation energy versus conversion plots for the epoxy systems studied.     

Performance of olive waste ash concrete exposed to elevated temperatures

This study explores the influence of olive waste ash (OWA) on the performance of concrete exposed to elevated temperatures in the range from 400 to 600 °C. The performance of concrete to elevated temperature was evaluated using compressive strength and electrical charge of concrete. Three OWA levels were used in the study: 7%, 15%, and 22% by weight of cement. The other experimental parameters investigated in the study were elevated temperature (400 and 600 °C), aggregate type (crushed basalt and volcanic tuff), w/c ratio (0.5 and 0.7), and air content (non-air and air entrained). After the initial moist curing period of 90 days, concrete specimens were exposed to elevated temperatures for a period of 2 h using an electric furnace.     

A compact CMOS DC-DC buck converter based on a novel complement value leaping PWM technique

A very compact ultra-low power DC-DC buck converter is presented. The proposed buck converter employs a novel complement value leaping pulse-width modulation (PWM) technique to realize the desired DC mean-value for various loads. Incorporating just two counters with a simple digital controller to load the repeatedly complemented value of the 4bit up/down counter as the initial value of the least significant bits of the 5bit up counter, a PWM pulse is created to manage the charge/recharge period. The realized PWM signal maintains the same desired output voltage mean value for any load resistance between 80 and 140 Ω. The switching frequency is 160 kHz, and the overall power consumption is 26.9 nW, while the efficiency is 93.4% for current range of 1.7 to 3 mA. The performance of the proposed converter is validated by Cadence post-layout simulations utilizing TSMC180nm CMOS technology for 1-V supply voltage providing the output voltage mean value of 0.24 V.