Journal of Basrah Researches (Sciences)

Sesarma boulengeri (Calman) crab populations were tested for food limitation in an intertidal flat in Shatt Al-Arab River. Food supply was artificially increased by adding thin - cut plants. This resulted in a relative increase in the crabs population density, recruitment and organic content. Crabs dig more burrows than they require for theis protection and their physiological needs; some time they may dig burrows in excess even when empty burrows are available in response to their food supply. The hypothesis was examined by comparing burrow and crab densities in an intertidal flat, then manipulating the burrow density and food availability in the laboratory. Furthermore, females were assumed to be more sensitive to the food availability than males and small crabs more sensitive than large crabs and the numbers of burrows were more than crabs. Smaller crabs of both sexes burrow faster and to lesser depths .New burrows despite the presence of unoccupied burrows and burrowing activity of smaller crabs of both sexes varied with food availability. The final results showed that the small crabs may be more sensitive to food availability and may be more capable of adjusting their burrowing activity to their food supply.

The behavior of nonlinear resonator(R,L and Varactor diode) series circuit are simulated in this paper using Electronics workbench program version 5.12 for two diodes ( BYW32 and BYW36 ).Unstable behavior was observed during the range of frequency ( F = 1.5X104 – 2X 105Hz) which the circuit behave randomly. It is not possible to measure VR,VL,VD and I exactly.

We have calculated the phase shifts and DCS’s for electrons scattered elastically from Helium atom by combining the exchange potential of Hara to Perdew and Wang correlation potential together with a parameter free polarisation potential, and the static potential. This model shows , a good agreement with the previous theoretical and in accord with the a vailable experimental values for many investigators.

The dielectric properties of poly ( 1,8-antraquinon phthalate film’s) have been studied through measuring the electrical equivalent circuit (lumped circuit ) contained capacitance and resistance. The measurements were carried out in temperature range ( 305-343)K, at constant frequency (1KHz). The permittivity was found decreased with increasing temperature similar to the CP , and the relaxation process was pointed in the temperature spectrum of the imaginary part of the dielectric constant ε= related to α- process. Another result that was obtained was the dissipation factor which at a high temperature decreased with increasing temperature.

Studies of chaos in electronic circuits and systems have shown that chaotic signals generated in these systems can potentially be used as carriers for information transmission in the communications systems. This paper demonstrates the generation of chaos in the Colpitts oscillator by using numerical simulation. The dynamics of the different voltages and the current through the inductor are calculated when the series resistance with inductor taken as a bifurcation element. The values of the emitter resistance that generate the chaotic behavior is investigated. The generation of chaos is confirmed by calculating the bifurcation diagram, phase portrait attractors, and three dimensional- attractors. The bifurcation diagram allows the classification of the regions of the different behaviors of oscillator (quasi-periodic oscillations and chaotic oscillations).

The effect of oxygen content on six samples of high temperature superconductor (HTS) Bi2Sr2CaCu2O8+δ (Bi:2212) was studied . As the sample oxygen content increases the value of condensation energy (which are calculated using the electronic specific heat and the entropy Ss of the superconducting phase) increases at the overdoped region . shows a maximum at the optimal doping (where and the hole concentration in CuO2 planes is ), at underdoped region decreases because of the effect of pseudo gap in the normal phase.

In this theoretical study Quantum efficiency (QE) was calculated numerically as a function of diffusion length ( Lp) ,wavelength (λ) and absorption depth (1/α) with different values of each of depletion width (w) , absorption coefficient (α). QE is a powerful tool to characterize ( CdS/CdTe) solar cell. In this study different value of these parameters were assumed to obtain a good QE of (CdS/CdTe) solar cell, also this study shows that the value of QE is (0.96) when (α=104 cm-1 ).

We have calculated the phase shifts, differential cross sections (DCS’s), total cross sections (TCS’s) and momentum transfer cross sections (MTCS’s) for the positrons scattered elastically from Ne, Ar, Kr and Xe atoms. The theoretical method is based on combining the static potential with the polarisation potential (containing both dipole and quadrupole polarisabilities) at long distances and with the correlation potential of Ashok Jain at short distances. We found a good general agreement with other experimental and theoretical values of many investigators.

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The Study of the effect of natural aging on some mechanical properties of (Al-Cu) & (Al-Zn) alloys

CuAl1-xFexS2 thin films have been prepared using the chemical spray pyrolysis technique with substrate temperature (Ts) at 593˚K for which x varies from 0 to1. The optical absorption at room temperature is studied for the different Fe concentrations. The electrical resistance is measured in the temperature range (300-400)˚K for different x values. The absorption optical spectra show two electronic transitions. The first is due mainly to the iron presence, which is around 2.55 eV, and is concentration independent. The second is concentration dependent changing from 3.35 eV for x=0 to 3.65 eV for x=1. The introduction of iron atoms into the ternary compound CuAlS2 has a drastic effect on the electrical properties: The amorphous samples go through a transition from semiconductor behavior to a semi-metallic one for x as low as 0.1.

CuAlS2:Mn thin films were prepared by spray pyrolysis technique. The prepared films were deposited on the glass substrate temperature Ts of 613οK. The optical properties were studied as a function of Mn doping concentration. The estimated direct energy gaps are in the range (3.29-2.92)eV for Mn concentration range (0.1-5) wt%. The DC electrical conductivity of pyrolytic-sprayed CuAlS2 thin films doped with Mn is measured in the temperature range (300-400οK). The doping concentration ranges from 0% to 5% by weight. In the lower temperature region, the conductivity and the activation energy are functions of doping concentration for less than 0.7%. However they are nearly constant for concentration more than 0.7%. In contrast for what is expected, the overall conductivity decreases with a doping concentration. Under the band model, the behavior of the electric conductivity is attributed to the existence of donor’s levels and the effect of replacement of Mn in the Al site as a favorable one.