Preparation and determination of rheological behavioour of fine strontium titanate powder suspensions

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 1999Includes bibliographical references (leaves: 70-74)Text in English; Abstract: Turkish and Englishx, 74 89 leavesIn this project, strontium titanate powders were prepared by using solgel and Pechini methods. In sol-gel method, the powders were prepared by mixing the Ti02 sol and Sr(N03h solution. Precipitation was observed after the addition of Sr(N03)2 solution. Two powders were prepared by each method. In sol-gel method, acid:alcohol ratio was changed. In Pechini method, 50% of citric acid was substituted with polyacrylic acid. The characterization of the powders were performed by Fourier Transform Infrared Spectrophotometer (FTIR), Thermogravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), X-Ray Diffraction and Optical Microscope. The calcination temperature of 650°C was chosen for sol-gel powder according to TGA data. XRD pattern showed that this temperature was not high enough to form complete SrTi03 phase, but no peaks related to nitrates or organic groups was observed in FTIR spectra. Sintering studies indicated that the agglomeration of sol-gel powder was very strong because the relative densities were very small. Pechini powders had weaker agglomerates and sintered to higher densities. The diameters of the Pechini powders were found as in the range of 0.2-0.5 um. The powders were dispersed in white oil and the rheological behaviour of these dispersions was studied by a rheometer. Several runs at different shear rates, and volume fractions were done. The suspensions without surfactant showed shear-thinning behavior, which indicates that the suspensions were flocculated. The addition of surfactant in certain amount produced stabilized suspenSIOns. The stabilized suspenSIOns showed Newtonian or Dilatant behaviour. The increase in the solids loading did not show significant change in the viscosity of stabilized suspension

Expectations of patients with hemiparesis from physiotherapy programme: concordance among patients, patients’ caregiver and physiotherapists

Purpose: The aim of this study was to examine the agreement between physiotherapists (PTS), patients and caregivers about the physiotherapy of patients with hemiparesis. Materials and methods: Fifty-two patients with hemiparesis (M¼24, F¼28), caregivers (N¼52) and PTs (N¼52) who applied for the physiotherapy programme were interviewed. Demographic and clinical characteristics of the patients were recorded. A questionnaire composed of six questions was used to describe the expectations of the PTs, caregivers and patients about the physiotherapy programme. Results: The Kappa calculator revealed a statistically moderate level of agreement between PTs and caregivers (K¼0.532, p¼.0001), patients and caregivers (K¼0.496, p¼.0001) and PTs and patients (K¼0.401, p¼.0001) regarding the expectations of physiotherapy programme. Conclusion: Expectations of the patients and caregivers must be considered for rehabilitation; hence, participation in the therapy and efficacy of the physiotherapy programme will increase. Consequently, we believe that the expectations of the patients and caregivers should be considered by the PTs when preparing a treatment programme for patients with hemiparesis

Effect of vortex generators to the flow around circular cylinder

Dairesel silindir etrafındaki akım, son derece karmaşık yapısı ve mühendislik uygulamalarında sıkça karşılaşılan bir akım tipi olması nedeniyle, yaklaşık bir asırdır hidro-aerodinamik alanda araştırmacıların temel konularından birisi olmuştur. Öte yandan, sınır tabaka ayrılması özellikle dolgun cisimler etrafındaki akışı değiştirerek büyük miktarda enerji kaybına yol açan bir olaydır. Buna bağlı olarak, hidro-aerodinamik pek çok aracın performansı akım ayrılmasının yeri tarafından kontrol edilmektedir. Akım ayrılmasının engellenmesi ya da geciktirilmesi için kullanılan en etkili yöntemlerden biri pasif girdap yaratıcılardır. Girdap yaratıcılar, neden oldukları sınır tabaka içine gömülen girdaplardan dolayı oluşan makro ölçekteki hareketler ile duvar yakınındaki akışın yeniden düzenlenmesini sağlamaktadır. Çalışmadaki amaç, girdap yaratıcıların dairesel silindir etrafındaki akışa ve girdap oluşma mekanizmasına olan etkilerinin deneysel olarak ortaya konmasıdır. Çalışmada, dairesel silindirin yakın iz bölgesi DPIV ile görüntülenmiştir. Deneyler, Newcastle Üniversitesi Emerson Kavitasyon Tüneli’nde gerçekleştirilmiştir. Çalışmada, 1.6 mm yüksekliğinde, akış yönüne ±10 derece açı yapacak şekilde kullanılan girdap yaratıcıların silindir çevresine dört farklı açıda yerleştirildikleri vakalar ve girdap yaratıcı içermeyen yalın silindir vakası yer almaktadır. Çalışmadaki Reynolds sayısı 41300 ve buna karşılık gelen silindir akış rejimi ise kritik-altı rejimdir. Ölçümlenen akış alanlarının analizi, Reynolds Ayrıştırması ve POD olmak üzere, iki ayrı türbülanslı akış alanı ayrıştırma tekniği ile gerçekleştirilmiştir. İz bölgesindeki girdaplılık, gerilme dağılımı, salınım frekansı gibi pek çok akış özelliği ortaya konmuştur. Yalın silindir vakası için yapılmış olan ölçümler literatür ile karşılaştırılmıştır. Girdap yaratıcıların etkisi, vakaların kendi aralarında ve yalın silindir ile karşılaştırmaları ile belirlenmiş, sonuçlar tartışılmıştır. Anahtar Kelimeler: Dairesel silindir etrafındaki akış, girdap yaratıcılar, DPIV.  Flow around a circular cylinder has been one of the basic research subjects in hydro-aerodynamics area in almost a hundred years. Related to its complex flow characteristics there are many aspects that make this topic most interesting including surface curvature of the cylinder, severe adverse pressure gradient, massive flow separation, oscillation of the separation point, unstable wake and hence vortex shedding, high sensitivity to free stream properties, aspect ratio, blockage, vortex street formation and completely variable flow pattern between flow regimes. Besides, boundary layer separation causes large energy losses especially by changing the flow pattern around bluff bodies. Accordingly, the performance of many hydro-aerodynamic vehicles is controlled by the location of the separation point. Thus, besides the importance of the separation control as a basic research subject, it can be regarded as an important engineering problem. One of the most effective methods used for preventing and delaying flow separation is the use of passive vortex generators. The macro scale motions of the vortices embedded in the boundary layer caused by the vortex generators provide over tuning of the flow in the vicinity of the wall. Thus, two important subjects of the fluid mechanics are considered in this study. The aim of the study is to experimentally investigate the effect of the streamwise vortex generators on the flow around circular cylinder and vortex formation mechanism. Wake oscillations of the circular cylinder and vortex shedding is visualized with digital PIV system which is the most suitable measurement system for determination of the general flow topology such as vortex structures and stress distribution. The experiments are conducted at Emerson Cavitation Tunnel, School of Marine Science and Technology, Newcastle University. The study consists of five cases including bare cylinder and four cases with vortex generators in which the generators are located at 50, 60, 65, and 70 degrees angles from the first stagnation point. The bare cylinder and vortex generators cases are coded as VG0000, VG1650, VG1660, VG1665, and VG1670, respectively. Vane type vortex generators which are 1.6 mm in height are paced with ±10 degrees sweep angles on the cylinder. The Reynolds number investigated is 41300, which corresponds to the sub-critical flow state. All the measurements were conducted at the midspan of the cylinder and the measurement area according to the cylinder diameter was 2.6Dx0.9D, in X and Y directions, respectively. The free stream velocity was 0.588 m/s and the inlet turbulence intensity and turbulence length scale of the free stream at this velocity were 1.73% and 0.22D, respectively. The analysis of the flow fields extracted from the PIV images are processed with two different turbulent flow field decomposition techniques including Reynolds decomposition, and Proper Orthogonal Decomposition (POD). The flow properties such as vorticity, stress distribution and oscillation frequency are derived from the analysis. The results of the measurements conducted for the bare cylinder are compared with the data in the open literature.  These indicate that the results are in good agreement with the results of the similar studies in literature. Experimental results show that the vortex generators highly affect the near wake and hence the boundary layer of the cylinder. First of all, Reynolds averaged flow fields indicate that the shear layers get closer to each other, bend towards the centerline, and the width of the near wake decreases. These events clearly indicate that the flow separation is delayed on the measurement plane. One can observe that the vortex formation length and the wake closure length are increased considerably with the downstream motion of the separation location as shown in the literature. The amount of the global mean circulation in the flow fields is also increased because of the vortex generators while the width of the shear layers is decreased. The more concentrated pattern of the shear layers provide the vortex formation process to occur at a longer distance from the cylinder. It is expected that the increase in the vortex formation length causes the low pressure area behind the cylinder to move with the vortices and hence decreases the suction at the rear side of the cylinder. With the displacement of the shear layers towards the wake centerline and the thinning of the shear layers, the Strouhal number is increased approximately 41% at VG1650, and then is decreased slowly probably due to the reduction of strength of the forming vortex. It is obvious that the strength of the stresses due to both turbulent and coherent motions decreases because of the vortex generators. Keywords: Flow around circular cylinder, vortex generators, DPIV. 

Large eddy simulations of the turbulent channel flow over dimpled surfaces

Reducing skin friction has a key role in the efficiency of rail, highway, and airway transport vehicles or naval systems such as ships and underwater vehicles. In recent years, there is a growing interest in investigating turbulent drag-reducing capabilities of dimpled surfaces, which have great potential as a passive solution, while there still exists highly conflicting views and drag reduction rates reported in the literature as well as a lack of information about the drag reduction mechanism. In this study, large-eddy simulations (LES) were performed to investigate the characteristics and physical mechanism of the fluid flow over dimpled surfaces in a fully developed channel flow. The Reynolds number based on the channel height and the mean bulk velocity was nearly 5600 for all cases examined. Within the framework of the study, various dimple depth to diameter ratios as well as different dimple arrangements and geometries were considered. The detailed mean and instantaneous flow fields, turbulent kinetic energy budget and spectral characteristics of the flow are presented. The study revealed the potential of the dimpled surface in reducing skin friction and provided critical information about the flow features affecting the performance of the dimples

The frequency of Duchenne muscular dystrophy/Becker muscular dystrophy and Pompe disease in children with isolated transaminase elevation: results from the observational VICTORIA study

IntroductionElevated transaminases and/or creatine phosphokinase can indicate underlying muscle disease. Therefore, this study aims to determine the frequency of Duchenne muscular dystrophy/Becker muscular dystrophy (DMD/BMD) in male children and Pompe disease (PD) in male and female children with isolated hypertransaminasemia.MethodsThis multi-center, prospective study enrolled patients aged 3–216 months with serum alanine transaminase (ALT) and/or aspartate transaminase (AST) levels >2× the upper limit of normal (ULN) for ≥3 months. Patients with a known history of liver or muscle disease or physical examination findings suggestive of liver disease were excluded. Patients were screened for creatinine phosphokinase (CPK) levels, and molecular genetic tests for DMD/BMD in male patients and enzyme analysis for PD in male and female patients with elevated CPK levels were performed. Genetic analyses confirmed PD. Demographic, clinical, and laboratory characteristics of the patients were analyzed.ResultsOverall, 589 patients [66.8% male, mean age of 63.4 months (standard deviation: 60.5)] were included. In total, 251 patients (188 male and 63 female) had CPK levels above the ULN. Of the patients assessed, 47% (85/182) of male patients were diagnosed with DMD/BMD and 1% (3/228) of male and female patients were diagnosed with PD. The median ALT, AST, and CPK levels were statistically significantly higher, and the questioned neurological symptoms and previously unnoticed examination findings were more common in DMD/BMD patients than those without DMD/BMD or PD (p < 0.001).DiscussionQuestioning neurological symptoms, conducting a complete physical examination, and testing for CPK levels in patients with isolated hypertransaminasemia will prevent costly and time-consuming investigations for liver diseases and will lead to the diagnosis of occult neuromuscular diseases. Trial RegistrationClinicaltrials.gov NCT04120168

Laser sistemlerinde kullaılan prizma ve aynaların yapıştırma bazlı optomekanik tutucularının analizi ve deneysel doğrulaması.

In this thesis, different optomechanical design and adhesive configurations for mounting mirrors and prisms used in a laser system are investigated. Maintaining stability and strength of optical components of a laser device is difficult especially if the system is to be used in military environment. In order to determine the strength of prism mounts to high acceleration levels, mathematical correlations derived by Yoder are used. By use of these mathematical correlations, safety factor of different prism mounts and adhesive configurations are calculated for an acceleration level of 40g. So as to decide most stable mirror mount and adhesive configuration, several experiments are conducted. For the experiments, 5 different optomechanical mounts are designed. Then, 25 mirrors are bonded to the designed mounts with 5 different adhesives. These experiments are done to simulate harsh military environmental conditions such as thermal shock, mechanical vibration and mechanical shock. In the experiments, angular movement of mirrors due to adhesive cure, thermal shock, mechanical vibration and mechanical shock are monitored. Thermal shock is applied between -40ºC and 70ºC with a temperature change of 22ºC/min. On the v other hand, mechanical vibration of 14 grms and mechanical shock of 40g for 6 ms is applied in the experiments. Shortly, this study is done for determination of the most stable mirror and prism mount design and adhesive combination of a laser system subjected to extremely harsh environments.M.S. - Master of Scienc

Preparation and determination of rheological behavioour of fine strontium titanate powder suspensions

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 1999Includes bibliographical references (leaves: 70-74)Text in English; Abstract: Turkish and Englishx, 74 89 leavesIn this project, strontium titanate powders were prepared by using solgel and Pechini methods. In sol-gel method, the powders were prepared by mixing the Ti02 sol and Sr(N03h solution. Precipitation was observed after the addition of Sr(N03)2 solution. Two powders were prepared by each method. In sol-gel method, acid:alcohol ratio was changed. In Pechini method, 50% of citric acid was substituted with polyacrylic acid. The characterization of the powders were performed by Fourier Transform Infrared Spectrophotometer (FTIR), Thermogravimetric Analyzer (TGA), Scanning Electron Microscope (SEM), X-Ray Diffraction and Optical Microscope. The calcination temperature of 650°C was chosen for sol-gel powder according to TGA data. XRD pattern showed that this temperature was not high enough to form complete SrTi03 phase, but no peaks related to nitrates or organic groups was observed in FTIR spectra. Sintering studies indicated that the agglomeration of sol-gel powder was very strong because the relative densities were very small. Pechini powders had weaker agglomerates and sintered to higher densities. The diameters of the Pechini powders were found as in the range of 0.2-0.5 um. The powders were dispersed in white oil and the rheological behaviour of these dispersions was studied by a rheometer. Several runs at different shear rates, and volume fractions were done. The suspensions without surfactant showed shear-thinning behavior, which indicates that the suspensions were flocculated. The addition of surfactant in certain amount produced stabilized suspenSIOns. The stabilized suspenSIOns showed Newtonian or Dilatant behaviour. The increase in the solids loading did not show significant change in the viscosity of stabilized suspension