Change in air temperature over Sudan and South Sudan with time and station coordinates and elevation during the last century

Annual mean air temperature for Sudan and South Sudan for the three periods 1900-1940, 1961- 1990 and 1981-2010 for 12 stations was analyzed with objectives of studying changes in air temperature over the area during the last century and also to study the linkages between mean, maximum and minimum air temperature on the one hand and latitudes, longitudes and elevations on the other hand. The data was obtained as normal data for each period from Sudan Meteorological Authority and other sources. The results showed an increase of about 0.60 degrees Celsius in the mean temperature of the 12 stations over the last century. The maximum temperature dropped in the second period by about 0.40 degrees Celsius and increased in the third period by about 0.35 degrees making almost no net change over the century.  The minimum temperatures increased on the average by about 1.2 degrees since the turn of the last century and increased by about 0.32 degrees between the last two periods. The net increase in air temperature for the 12 stations over the last century was mainly a result of an increase in the minimum air temperature. The results also showed strong linkages between mean and minimum temperatures on one hand and longitudes on the other hand. Keywords: Air temperature, Variation, Coordinates, Elevation, Suda

Heat Pipes for Computer Cooling Applications

There is an increasing demand for efficient cooling techniques in computer industry to dissipate the associated heat from the newly designed and developed computer processors to accommodate for their enhanced processing power and faster operations. Such a demand necessitates researchers to explore efficient approaches for central processing unit (CPU) cooling. Consequently, heat pipes can be a viable and promising solution for this challenge. In this chapter, a CPU thermal design power (TDP), cooling methods of electronic equipments, heat pipe theory and operation, heat pipes components, such as the wall material, the wick structure, and the working fluid, are presented. Moreover, we review experimentally, analytically and numerically the types of heat pipes with their applications for electronic cooling in general and the computer cooling in particular. Summary tables that compare the content, methodology, and types of heat pipes are presented. Due to the numerous advantages of the heat pipe in electronic cooling, this chapter definitely leads to further research in computer cooling applications

Split-step Approach to Electromagnetic Propagation through Atmospheric Turbulence using the Modified von Karman Spectrum and Planar Apertures

The impact of atmospheric phase turbulence on Gaussian beam propagation along propagation paths of varying lengths is examined using multiple random phase screens. The work is motivated by research involving generation and encryption of acousto-optic chaos, and the interest in examining propagation of such chaotic waves through atmospheric turbulence. A phase screen technique is used to simulate perturbations to the refractive index of the medium through the propagation path. A power spectral density based on the modified von Karman spectrum model for turbulence is used to describe the random phase behavior of the medium. In recent work, results for the numerical simulation of phase turbulence over a narrow region of space implemented by placing a planar aperture representing a (narrow) random phase screen were presented. Results are presented pertinent to extended phase screens (via multiple random-phase apertures) through which an incident Gaussian beam propagates incrementally via alternate phase transmission and diffraction along the propagation path. Additionally, for profiled electromagnetic waves (such as Gaussian), the scintillation index is evaluated for extended phase turbulence, and finally, fringe visibility due to the interference of double-Gaussian beams passing through extended turbulence is examined

Diffractive Propagation and Recovery of Modulated (including Chaotic) Electromagnetic Waves through Uniform Atmosphere and Modified von Karman Phase Turbulence

In a parallel approach to recently-used transfer function formalism, a study involving diffraction of modulated electromagnetic (EM) waves through uniform and phase-turbulent atmospheres is reported in this paper. Specifically, the input wave is treated as a modulated optical carrier, represented by use of a sinusoidal phasor with a slowly timevarying envelope. Using phasors and (spatial) Fourier transforms, the complex phasor wave is transmitted across a uniform or turbulent medium using the Kirchhoff-Fresnel integral and the random phase screen. Some preliminary results are presented comparing non-chaotic and chaotic information transmission through turbulence, outlining possible improvement in performance utilizing the robust features of chaos

Modeling of Power Spectral Density of Modified von Karman Atmospheric Phase Turbulence and Acousto-Optic Chaos using Scattered Intensity Profiles over Discrete Time Intervals

In recent research, propagation of plane electromagnetic (EM) waves through a turbulent medium with modified von Karman phase characteristics was modeled and numerically simulated using transverse planar apertures representing narrow phase turbulence along the propagation path. The case for extended turbulence was also studied by repeating the planar phase screens multiple times over the propagation path and incorporating diffractive effects via a split-step algorithm. The goal of the research reported here is to examine two random phenomena: (a) atmospheric turbulence due to von Karman-type phase fluctuations, and (b) chaos generated in an acousto-optic (A-O) Bragg cell under hybrid feedback. The latter problem has been thoroughly examined for its nonlinear dynamics and applications in secure communications. However, the statistical characteristics (such as the power spectral density (PSD)) of the chaos have not been estimated in recent work. To that end, treating the chaos phenomena as a random process, the time waveforms of the chaos intensity and their spectra are numerically evaluated over a (large) number of time iterations. These spectra are then averaged to derive the equivalent PSD of the A-O chaos. For the turbulence problem, an optical beam passing through an input pinhole is propagated through a random phase screen (placed at different locations) to a desired distance (typically near-field) under different levels of turbulence strength. The resulting spatial intensity profile is then averaged and the process repeated over a (large) number of pre-specified time intervals. From this data, once again, the turbulence PSD is calculated via the Fourier spectra of the average intensity snapshots. The results for the two systems are compared

Spectral and Performance Analysis for the Propagation and Retrieval of Signals from Modulated Chaos Waves Transmitted through Modified von Karman Turbulence

A transfer function formalism is applied to track propagation of modulated chaos waves through modified von Karman phase turbulence; the demodulated signal is examined vis-à-vis performance relative to turbulence strength in comparison with non-chaotic propagation

A Transfer Function Based Frequency Model for Propagation of a Chaos Wave through Modified von Karman Turbulence under Various Chaos and Turbulence Conditions

Complex phasor fields for electromagnetic wave propagation through von Karman turbulence and acousto-optic RF chaos are derived en route to the effective transfer function between chaos and narrow turbulence. Results are tested for several turbulence and chaos conditions

Investigation of Profiled Beam Propagation through a Turbulent Layer and Temporal Statistics of Diffracted Output for a Modified von Karman phase Screen

Gaussian beam propagation through a turbulent layer has been studied using a split-step methodology. A modified von Karman spectrum (MVKS) model is used to describe the random behavior of the turbulent media. Accordingly, the beam is alternately propagated (i) through a thin Fresnel layer, and hence subjected to diffraction; and (ii) across a thin modified von Karman phase screen which is generated using the power spectral density (PSD) of the random phase obtained via the corresponding PSD of the medium refractive index for MVKS turbulence. The random phase screen in the transverse plane is generated from the phase PSD by incorporating (Gaussian) random numbers representing phase noise. In this paper, numerical simulation results are presented using a single phase screen whereby the phase screen is located at an arbitrary position along the propagation path. Specifically, we examine the propagated Gaussian beam in terms of several parameters: turbulence strength, beam waist, propagation distance, and the incremental distance for Fresnel diffraction for the case of extended turbulence. Finally, on-axis temporal statistics (such as the mean and variance) of the amplitude and phase of the propagated field are also derived

Performance of Different Tomato Genotypes in the Arid Tropics of Sudan during the Summer Season. I. Vegetative Growth

Selected, eleven tomato genotypes of diverse origin were grown in a glasshouse of the Humboldt University of Berlin, Germany during 2002 and under field conditions in Shambat, University of Khartoum, Sudan for two successive seasons (2002/2003, 2003/2004). High temperatures under field conditions resulted in poor stand and stunted growth of tomato plants. Highly significant differences were encountered among the different genotypes for leaf area, leaf area ratio, leaf weight ratio, stem fresh and dry weight and leaf fresh and dry weight. Based on results obtained from this study, the genotype ‘Summerset’ proved to be more tolerant under high temperature conditions in comparison to other investigated genotypes and may be useful for exploitation under arid tropical region of Sudan

Practical approach to predict the shear strength of fibre-reinforced clay

yesCarpet waste fibres have a higher volume to weight ratios and once discarded into landfills, these fibres occupy a larger volume than other materials of similar weight. This research evaluates the efficiency of two types of carpet waste fibre as sustainable soil reinforcing materials to improve the shear strength of clay. A series of consolidated undrained (CU) triaxial compression tests were carried out to study the shear strength of reinforced clays with 1%, to 5% carpet waste fibres. The results indicated that carpet waste fibres improve the effective shear stress ratio and deviator stress of the host soil significantly. Addition of 1%, 3% and 5% carpet fibres could improve the effective stress ratio of the unreinforced soil by 17.6%, 53.5% and 70.6%, respectively at an initial effective consolidation stress of 200 kPa. In this study, a nonlinear regression model was developed based on a modified form of the hyperbolic model to predict the relationship between effective shear stress ratio, deviator stress and axial strain of fibre-reinforced soil samples with various fibre contents when subjected to various initial effective consolidation stresses. The proposed model was validated using the published experimental data, with predictions using this model found to be in excellent agreement