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One of the goals in solid rocket motor design is to have as large volumetric loading as possible keeping the basic requirements unaffected. Slotted grain can achieve this goal as it has the advantages of sliver-free and no stress-concentration regions that occur in other internal burning grains as star grain and wagon wheel grain. It has the disadvantage of exposing the motor wall to hot gases. In this paper, the geometry of slotted grain is discussed and the effect of design parameters (e.g., number of slots, dimensions of the slot, etc.) of slotted grain on grain burn back is explained. Also, a comparison between results and experimental data is performed.

Propellant ignition is an essential process in solid rocket motor operation as it is responsible of starting the combustion and to reliably self-sustain burning of the solid propellant. Despite the importance of igniter design and ignition process, the relations dealing with igniter mass determination are not well studied and not validated against actual motors with a systematic variation of parameters. The main objective of the current research is to validate the available equations in open literature for determination of the mass of igniter pyrotechnic charge. Data from seven real solid propellant rocket motors were used to validate the relations. These motors have different sizes, grain geometries and pyrotechnic compositions. The results show that the equation of Brayan–Lawerene has the smallest root mean square error (RMSE), and so, it is considered more convenient.

One of the great challenges in designing tactical solid missiles is to achieve high acceleration in the boost phase then maintaining constant speed during the sustain phase. This could be achieved by using a dual thrust solid-propellant rocket motor. Many of these tactical motors use a combination of star, tubular or finocyl grains to achieve this profile. The present study uses two tandem star grains with different design parameters and different transition geometry. Previous researches had consistently shown that the main advantage of star grain is the potential higher volumetric loading in addition to high tailorability. The pressure-time curve for the designed grains is calculated using a zero-dimensional internal ballistic module and a small-scale test motor is used to verify the calculated pressure-time curve. Different transition geometries are compared. Tapered transition is shown to give a comparable performance with the sharp transition with the advantage of higher volumetric loading.

Centrifugal pumps (CP) are probably among the most often used machinery in industrial facilities as well as in common practice. Compared to other types of rotating pumps, CP yield higher efficiency. In aerospace application, reducing the weight of the CP impeller has the advantage of reducing mechanical stresses and enable using the CP at the high number of revolutions. In order to minimize the impeller weight the requirements to study and develop the CP with semi-open impeller appear. The present paper is devoted to revealing more details about the impact of CP side clearance on its performance. This is done by numerically investigating the influence of the variation of the CP side clearance width (0:0.2 impeller width) on the CP performance parameters at different flow rates (0:5 L/s). These CP performance parameters include the pump head, efficiency, slip factor, blade loads and the internal flow structure. The numerical simulation has been compared with own experimental results and a published empirical formula to verify the numerical solution. The CFD results show an acceptable agreement with the results of the experimental work and the empirical formulas. It has been shown that the impeller side clearance has a great regression effect on the centrifugal pump performance.

The effect of impeller side clearance (the gap between the impeller face and the casing) on the centrifugal pump performance has been investigated numerically through monitoring the change of the pump head and efficiency at different flowrate. 3-D numerical simulation has been carried out using commercial software, ANSYS® CFX. The numerical simulation has been compared with experimental results to verify the numerical solution. In addition, the results have been compared with the closed impeller with front shroud at the same operating conditions It has been shown that the impeller side clearance have a great regression effect on the centrifugal pump performance. This regression on performance could be attributed to the drop in the pressure difference between the impeller inlet and outlet. And the secondary flow across the blade tip which impedes the core flow.

The effect of impeller blades shape modification on the centrifugal pump performance has been investigated numerically. Impeller blades’ shape have been modified by new technique called “bladelet”. This technique has been called the “bladelet” after the name of the aeroplane winglet because of the great similarity between them in shape and function. The shapes of the blade trailing edge greatly affect the performance of the turbomachines. So, the purpose of the blade tilting (bladelet) is to decrease the recirculating flow at the pump trailing edge due to the high pressure difference and enhance the hydraulic performance of the centrifugal pump. The bladelet technique has two main geometrical parameters: radial position RBL and bladelet inclination angle θBL. 3-D validated numerical simulation model has been carried out using commercial software, ANSYS® CFX, to study the effect of the bladelet technique and its different parameters on the pump performance at different flow rates. In this study nine cases with different bladelet parameters have been numerically simulated in order to check its effect on the centrifugal pump performance. These nine cases have been chosen by considering the geometrical constrain of the bladelet parameters. The results of these nine cases have been compared with the basic impeller (the same impeller but without bladelet) at the same operating condition in order to discuss the effect of the bladelet parameters variation on the centrifugal pump performance. It was found that the use of the bladelet technique decrease the pressure difference between the pressure and the suction side at the blade trailing edge. This decrease in pressure difference at the blade trailing edge decreases the flow recirculation at the impeller outlet from pressure side to suction side. Also, bladelet technique improves the hydraulic efficiency at the part-load operating zone. In addition, the bladelet has a regression effect on the pump head for some cases with high inclination angle and low radial position. However, the bladelet technique increases the impeller blades’ overlap.

In many applications, a constant thrust of the solid propellant rocket motor (SPRM) throughout the operating time is desired. Such thrust-time scenario is known as neutral burning. Typically, tubular grains with internal burning surface yield a progressive thrust-time history and, therefore, if a neutral thrust-time history is required, the progression in the burning surface should be compensated by including the side faces as well. However, neutrality of tubular grain that burns at both of the internal and end surfaces is subject to a limited range of slenderness ratio. Tapering the port at the end faces of the tubular grain would expand the range of the slenderness ratio that ensures neutrality. In the present paper, the issue of neutrality of taper-ended tubular grain is explored. For the studied case, it was found that with normal-ended tube grains neutrality can be realized for slenderness ratio 1.8 and web-to-radius ratio 0.4. However, keeping the same web-to-radius ratio and tapering the ends at angle 25 would slightly worsen the volumetric filling coefficient ( 15% less), but burning neutrality could be attained for slenderness ratios as high as 2.54 ( 40% higher). With this practice, it is possible to maintain neutrality where much longer grains may be adopted for certain applications.

Centrifugal pumps (CP) are probably among the most often used machinery in industrial facilities as well as in common practice. Compared to other types of rotating pumps, CP yield higher efficiency. In aerospace application reducing the weight of the CP impeller has the advantage of reducing mechanical stresses and enable using the CP at high number of revolution. In order to minimize the impeller weight the requirements to study and develop the CP with semi-open impeller appears. Using this type of impeller results in clearance between the impeller blades and the casing which degrade the centrifugal pump performance. The impact of this side clearance has not been deeply investigated in open literature. The present paper is devoted to reveal more details about the impact of CP side clearance on its performance. This is done by numerically investigating the influence of the variation of the CP side clearance width (0:0.2 impeller width) on the CP performance parameters at different flow rates (0:5 Liter/s). These CP performance parameters include the pump head, efficiency, slip factor, blades loads and the internal flow structure. 3-D steady numerical simulation has been carried out using commercial software, ANSYS® CFX. The computational domain consists of four zones: inlet, side gab, impeller and volute with outlet. They are defined by means of the multi-reference frame technique. The impeller is situated in the rotating reference frame, while the inlet, side gab and outlet zones are in the fixed reference frame, and they are related to each other through the “frozen rotor” interface. The meshes of four computational domains are generated separately after performing mesh sensitivity analysis. The boundary conditions are set as total pressure at inlet and the mass flow at outlet. A no-slip condition is imposed at the wall boundary defined at the blade and casing. A turbulent, incompressible flow solver has been adapted using SST k–ω turbulent model. The numerical simulation has been compared with own experimental results and a published empirical formulas to verify the numerical solution. The CFD results show an acceptable agreement with the results of the experimental work and the empirical formulas. It has been shown that the impeller side clearance have a great regression effect on the centrifugal pump performance. An explanation to the performance regression has been proposed based on the flow field feature. Performance regression could be attributed to the drop in the pressure difference between the impeller inlet and outlet. And the redistribution of the velocity inside the impeller channel and the side clearance.

This paper is concerned with identifying and quantifying the deterministic (as opposed to statistical) size effect in the strength of cracked concrete structures that is believed to be a result of stress discontinuities introduced by the cracks. For this, the strength of geometrically similar pre-cracked specimens of varying sizes made from three concrete mixes is measured in three-point bend and wedge splitting geometries. The true, size-independent specific fracture energy and the corresponding tension softening diagram of each of the three mixes are independently established in order to exclude their influence on the strength size effect. The test results show that the deterministic strength size effect weakens as the size of the crack reduces. This is confirmed by theoretical/computational studies based on the fictitious crack model in the range of sizes tested in the laboratory. The theoretical/computational model has been extended beyond this limited range to include cracked concrete structures in the size range 1:80. The computational results have been fitted by a simple strength size effect formula with appropriate asymptotic behaviour at both size extremes. The three unknown coefficients in this formula depend only on the size of the crack and they can be obtained by conducting tests on geometrically similar specimens of any shape but of varying sizes that can be conveniently handled in a laboratory. The three material properties of the concrete mix appearing in this formula, namely the Young modulus E, the direct tensile strength ft and the size-independent specific fracture energy GF must be independently measured. D 2005 Elsevier Ltd. All rights reserved.

The stress intensity factor (SIF) and the coefficients of higher order terms of the crack tip asymptotic field of typical wedge splitting specimens with two different loading arrangements are directly computed using a hybrid crack element. Accurate analytical expressions for the first five terms are obtained by fitting the computed data. Numerical results show that the coefficients of terms higher than three are negligibly small, this may explain that the wedge splitting specimen is more stable than other geometries. The first five terms are not sensitive to support conditions. However, for short cracks coefficients of terms, except the SIF, are quite sensitive to the loading arrangement even when the loads are statically equivalent.

This paper will report on an experimental investigation into the size effect in the strength of hardened cement paste (nominal compressive strength 40 MPa) and high strength concrete (nominal compressive strength 110 MPa) as measured in three point bending. The aim of the investigation is to judge the range of applicability of the various size effect formulae available in the literature. With this aim in mind, the failure loads have been analysed according to the size effect formulae of Bazant and of Karihaloo for the notched beams and according to those of Bazant and of Carpinteri for the unnotched beams. The results of this analysis will be presented. Improvements to Karihaloo’s size effect formula will also be proposed.

The centrifugal pump performance depends to great extent upon the flow pattern in the impeller passages. When the pump operates at small flow rates, the problem of circulation due to vortex formation in the impeller passages is found. A new method is introduced to control and reduce the size of generated vortices in the impeller passages. Slots are opened in the impeller vanes to allow fluid to flow from the pressure side to the suction side of the vane. The bleeding fluid could reduce the size of the vortices. It is found to depend mainly upon the length and the position of the slot. In the present work, the flow field is solved in the radial impeller passages using the stream function and the primitive variable approaches, to solve the flow equations. The flow pattern is used to compare the vortex size and the pump head for both cases with and without slotted impeller vanes at different slot sizes and at different positions. The slot position that produces the highest pump head, the slot length has been changed until the smallest vortex size is achieved. The numerical solution is introduced in a code program form, which is written in the Microsoft Visual C++ 6 language. Finally the optimum position and length of the slot is obtained at Rs/R2 = 0.4981, and with L /(R2-R1)= 0.2291. The model has been validated by comparison to a published experimental result of the same pump (for the same research program).

A theoretical investigation has been made to predict the flow pattern within a radial blade centrifugal pump. A mathematical model based on steady two-dimensional incompressible Navier-Stokes (N-S) equations has been developed. The real flow was modeled under these considerations. A computational-fluid-dynamic scheme was suggested using the primitive variables with artificial compressibility. The predictor-corrector method proposed by MacCormack was employed for its advantages of accuracy, less complexity, reasonable storage and convenient stability limit. A stability criterion was suggested and a fourth-order extrapolation smoothing term was used to limit the higher variations of the primitive variables. The use of this technique involved imaginary rows behind walls, and periodic boundaries at far upstream and downstream which adequately improved the convergence to the solution. Based on this model a computer program capable of predicting the flow pattern and pump characteristics inside the radial blade pump has been developed. The validity of the developed computer program, has been proven by comparing calculated and measured pump characteristic, which showed good agreement.

This study was done in Wad-Medani town in the central Sudan. A household survey and a hospital survey were conducted using structured questionnaires to assess household expenditure on malaria case management. A total of 360 cases of malaria were reported in the household survey. They were assessed by a questionnaire focused on household income daily expenditure and resources), with special attention to treatment and cost incurred. Also, a random sample of malaria cases hospitalized in the medical, obstetrical and paediatric wards in Wad-Medani hospitals were interviewed, comprising 75 adult patients and 75 children. Cases in the house survey were treated in health centers, private clinics, health insurance facilities or by self-medication. The mean expenditure on diagnosis and treatment of an episode of malaria was US dollars 5.12 for home-treated cases and US dollars 17.2 for a hospitalized case, representing a significant economic burden to family income. This cost varied according to type of treatment, type of health care provider and in hospitalized versus home-treated cases.

Phthirus pubis, Linnaeus 1758 that causes phthiriasis is a common infestation disease. However, it is commonly be acquired in jails, brothels, and other similar places. The efficacy of four insecticides commercially known as Eurax, Elimite, Licid, and Benzanil was evaluated for controlling pubic lice in vitro. The four test insecticides proved to be very effective. However, they differed in time needed for causing 100 percent mortality and they could be arranged descendingly as follows: Licid, Eurax, Elimite, and Benzanil.

The metacercariae of genus Brachylaima were collected from the kidney of the land snail Monacha obstructa. About thirteen to fifteen metacercariae were collected from each snail. The metacercariae observed were elongated rather than oval. The gonads were no so developed inspite of the great similarity between this larval stage and the adults. No larval stages rather than the metacercariae were observed. The specimens were examined in fresh status and then stained with carmine and fast green as counter stain. The excretory system was developed to very great extent. This seems to be the first record of this larval stage in Egypt since 1899 when Looss collected the adult of B. aequans from Gerbillus aegyptiacus. The heavy infection of snails reflects the higher incidence of this parasite among land snails as intermediate host. Since, the life cycle of this parasite is not yet confirmed experimentally in Egypt, the species has not been identified.

Serum levels of TNF-alpha was quantitatively estimated by the use of solid enzyme amplified sensitivity immunoassay (EASIA) in different stages of schistosomiasis mansoni, rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and schistosomal arthropathy. Statistically, significant higher levels were detected in the different groups compared to the normal control group. The level was found highest in hepatosplenic schistosomiasis with ascites (group 1c). The difference was significantly higher compared to cases of early S. mansoni infection (group Ia) and insignificant compared to hepatosplenic schistosomiasis without ascites (group 1b). No significant difference was detected comparing groups 1a and 1b, or groups 2a (RA) and 2b (SLE). Cases of schistosomal arthropathy (group 3) showed significantly higher level compared to groups 1a and 1b, although the level in group 1c was still significantly higher compared to group 3, the level was also significantly higher in group 3 compared to cases of RA but not to cases of SLE.

Parasitological and serological examination was done for 111 cases with various types of malignancies under immunosuppressive therapy and another 20 apparently healthy individuals as a control group to determine the prevalence of opportunistic parasitic infections among immunocompromised patients. Single examination showed that 74 (66.7%) harboured infection with different parasites: Strongyloides stercoralis infection was found in 4 (3.64%) cases; 3 cases (2.7%) had Pneumocystis carinii infection. No Cryptosporidium oocysts were detected; IFAT for toxoplasmosis was positive in 40 cases (36%) with titres ranging from 1/16 - 1/256 but IFAT-IgM was negative. The control group did not show any parasitic infection except that IFAT was positive in 4 out of 20 (20%) with titres ranging from 1/16 to 1/128 but IFAT-IgM was also negative. Although Toxoplasma infection was higher among patients the difference was insignificant. Generally the percentages recorded for the different parasites were found to be within the expected prevalence. One case report of concomitant opportunistic Pneumonocytis and Toxoplasma infection is reviewed.

A study has been done to find the effect of purification of crude antigens, extracted from adult Fasciola gigantica and Fasciola hepatica worms on the sensitivity of some serological techniques in diagnosis of fascioliasis. Using C.I.E.P. test, the partially purified antigens of both Fasciola species were less sensitive than their corresponding crude ones. Using I.H.A., the difference between results of crude and partially purified antigens for the two species were statistically insignificant, both (P greater than 0.05). So in applying this test, there is no need for the partially purification of antigen. On using E.L.I.S.A. the partially purified antigens showed higher sensitivities for detection of fascioliasis than their corresponding crude ones. Partially purified F. gigantica and F. hepatica antigens gave nearly the same results whether using C.I.E.P., I.H.A. or E.L.I.S.A. However, E.L.I.S.A. was the most sensitive technique followed by I.H.A. then C.I.E.P.

One of the main problems encountered by the surgeon are visceral adhesions after abdominal surgery. This problem was studied in animal experiments by inducing peritoneal adhesions in 30 albino rats. The anti-inflammatory, resp. anti-adhesive effect of corticosteroids and antihistamines was tested by application of these drugs before, resp. after surgery. Anti-inflammatory proteolytic enzymes (Wobe-Mugos) were applied pre-, resp. postoperatively in two other groups. A fifth group served as controls. A modified cotton-pellet technique was used for the experiments. The best results were achieved when "Wobe-Mugos" was applied after surgery.

In a recent paper, Abdalla and Karihaloo confirmed the boundary effect hypothesis of Hu and Wittmann and observed that a size-independent specific fracture energy GF of concrete could be obtained by testing three point bend (TPB) or wedge splitting (WS) specimens containing either a very shallow or a deep starter notch. This observation was based on TPB and WS tests on limited number of specimens. In this paper, we have re-evaluated 26 test data sets on specific fracture energy of concrete published in the literature to assess the validity of this observation. The re-evaluation is found to support this observation. The determination of the true specific fracture energy GF of concrete thus becomes a simple and straightforward task requiring very few specimens of the same dimensions and shape. This re-evaluation also provides guidance for the selection of the specimen dimensions depending on the maximum size of aggregate used in the concrete mix in order to obtain its true GF.

Three-point bend (TPB) and wedge splitting (WS) tests have been conducted on three different concretes and the specific fracture energy GF determined on the basis of the concept of local fracture energy. The latter is influenced by the free back surface of a notched test specimen, as explained by Hu and Wittmann. Tests on three or four specimen sizes with four notch to depth ratios confirm the idea of Hu and Wittmann that the size-independent specific fracture energy GF can be determined from measured fracture energy values that vary with the size of the specimen, W, and notch to depth ratio, a/W. More importantly, it is shown that the same size-independent GF can also be obtained by testing a single size specimen with only two notch to depth ratios, provided they are well separated (a/W = 0·05 and 0·50 in TPB, and 0·2 and 0·5 in WS), thus greatly simplifying the determination of the size-dependent fracture energy GF.

For the analysis of cracked concrete structures using the fictitious crack model two fracture properties of concrete are required, namely its true specific fracture energy GF and the corresponding tension softening relation σ(w). In a recent paper, the authors proposed a simple method for the determination of the true specific fracture energy of a concrete mix. In this paper a method is proposed based on the concept of a non-linear hinge for constructing a bilinear approximation of the tension softening relation consistent with the true specific fracture energy GF. The parameters of this bilinear approximation are inferred in an inverse manner. It is shown that this inverse identification procedure predicts accurate bilinear softening relations of concrete mixes tested in three-point bend and wedge-splitting modes.