Effects of Metal Oxide Nanoparticle Catalysts on the Diameter of Carbon Nanotubes Produced Via Pulsed Laser Ablation Deposition Technique

In this research work, bismuth oxide (Bi2O3) and nickel oxide (NiO) nanoparticles were synthesized through precipitation method, while iron oxide (Fe2O3) nanoparticles were synthesized via citrate pyrolysis. All the as-prepared metal oxide nanoparticles were used as catalysts for the growth of carbon nanotubes via pulsed laser ablation deposition (PLAD) technique. Pellets were first prepared from a mixture of 90 wt% graphite and 10 wt% catalysts in each case, and used as a target. An Nd: YAG laser with wavelength of 532nm and power of 10.24W was used to ablate the target materials, using a frequency of 5 kHz and current of 25A. The target materials were evaporated and transported to the substrate under the influence of argon. The expelled carbon precipitated and diffuses through the metal oxide catalysts and condensed on the substrate as carbon nanotubes. The effect of each of the catalyst on the diameter of the as-grown carbon nanotubes was investigated and the correlation between the type and the particle size of the catalysts and the diameter of the grown CNTs were studied. The results show that, there is a strong correlation between the diameter of the starting catalyst, with the diameter of the resulting carbon nanotubes for both Bi2O3 and Fe2O3, indicating that both catalysts serve as the nucleation point for the CNTs growth. However, the case of NiO shows a significant difference, as the diameter of the as-grown CNTs was eight times bigger than the size of the starting catalyst. This can be attributed to the aggregation of the as-prepared NiO particles to form bigger clusters, consequent to the ablation process. Bamboo-like CNTs were observed for Fe2O3 and NiO, which is attributed to the high cooling rate of the reaction chamber. Further contribution to this structure is the large pulse-to-pulse width of the system (140ns). However CNTs catalyzed by Bi2O3 were defect free tubes which can be attributed to the lower melting point of Bi2O3 compare to other catalysts used, thus forming CNTs at a lower eutectic temperature. From the results, it can be concluded that, for applications that requires a short tube with relatively large diameter Bi2O3 is the best catalyst. For long CNTs with relatively large diameter for encapsulation purposes, NiO is the best catalyst, while Fe2O3 was seen to be the best catalyst for catalyzing CNTs with a narrow diameter

The Study on Opportunities and Challenges of Productive Safety Net Program/PSNP/ in Southern Ethiopia: A Case Study of Three Selected Woreda’s in Wolaita Zone

The study discussed the opportunities and challenges of Productive Safety Net Programme in three selected districts in Wolaita zone, Ethiopia. The study utilized cross sectional survey research design to attain the objectives. Primary and secondary data were used and analyzed by using SPSS, version 20. Sample size determined by using Cochran formula (Cochran 1963:75) and 374 households selected using multistage sampling techniques. According to the study, the major opportunities of the programme to poor households are saving life of poor households, economic changes at household and community level, the changes in social inclusion, gender equality and community health and nutrition. The key challenges of the PSNP are targeting, cash transfer problems, and low economy base of the poor households, low graduation performance and weak management of appeals. The study proposed the way forward to enhance the opportunities and to minimize the challenges faced at the implementation stage of the programme. Keywords: Opportunities, Challenges, Productive safety net DOI: 10.7176/DCS/10-4-02 Publication date: April 30th 2020

Effects of sintering temperature on grain growth and the complex permeability of Co0.2Ni0.3Zn0.5Fe2O4 material prepared using mechanically alloyed nanoparticles.

Nanoparticle-sized Co0.2Ni0.3Zn0.5Fe2O4 was prepared using mechanical alloying and sintering. The starting raw materials were milled in air and subsequently sintered at various temperatures from 600 to 1300 °C. The effects of sintering temperature on physical, magnetic and electrical characteristics were studied. The complex permittivity and permeability were investigated in the frequency range 10 MHz to 1.0 GHz. The results show that single phase Co0.2Ni0.3Zn0.5Fe2O4 could not be formed during milling alone and therefore requires sintering. The crystallization of the ferrite sample increases with increasing sintering temperature; which decrease the porosity and increase the density, crystallite size and the shrinkage of the material. The maximum magnetization value of 83.1 emu/g was obtained for a sample sintered at 1200 °C, while both the retentivity and the coercivity decrease with increasing the sintering temperature. The permeability values vary with both the sintering temperature and the frequency and the absolute value of the permeability decreased after the natural resonance frequency. The real part of the permittivity was constant within the measured frequency, while the loss tangent values decreased gradually with increasing frequency

Occipital lobe infarctions are different

Halvor Naess, Ulrikke Waje-Andreassen, Lars ThomassenDepartment of Neurology, Haukeland University Hospital, University of Bergen, N-5021 Bergen, NorwayObjectives: We hypothesized that occipital lobe infarctions differ from infarctions in other locations as to etiology, risk factors and prognosis among young adults.Methods: Location, etiology, risk factors and long-term outcome were evaluated among all young adults 15–49 years suffering from cerebral infarction in Hordaland County, Norway between 1988 and 1997.Results: The following variables were more frequent among patients with occipital lobe infarction compared with patients with infarctions located elsewhere: younger age (P < 0.001), female sex (P = 0.016), prothrombotic state (P = 0.005) and lack of hypertension (P = 0.001). There was no difference as to long-term mortality or recurrence of cerebral infarction. Conclusion: Occipital lobe infarctions differ from infarctions in other locations among young adults. This may have important etiologic and therapeutical implications that need further studies.Keywords: cerebral infarction, occipital lobe, young adult

Observation of cotton-like bismuth oxide (β-Bi2O2.5) prepared via pulsed laser ablation deposition

Monoclinic bismuth oxide (α-Bi2O3) nanoparticles were prepared via precipitation method and irradiated with a pulsed laser forming thin films. Their phase and surface morphological properties were investigated using x-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). The XRD analysis shows the phase transformation to a partially crystalline tetragonal phase β-Bi2O3 thin film. The SEM micrograph of the nanoparticles, with an average crystal size of 72 nm, was seen to form a thin film with a peculiar structure, coined as “cotton-likeâ€�, is attributed to the high surface energy absorbed by the nanoparticles during ablation. The HR-TEM micrograph shows the particulate with a clearly defined interlayer spacing

Early ischemic CT changes before thrombolysis: The influence of age and diabetes mellitus

Lars Thomassen, Ulrike Waje-Andreassen, Halvor NaessDepartment of Neurology, Haukeland University Hospital, Bergen, NorwayObjectives: The significance of early ischemic changes (EIC) on computed tomography (CT) within 3 hours after stroke onset remains controversial. The semi-quantitative Alberta Stroke Program Early CT Score (ASPECTS) is found to have prognostic value in early stroke. This study assesses factors associated with the presence of EIC and the relation between EIC and clinical outcome.Materials and methods: CT scans from 61 consecutive patients receiving thrombolytic therapy were reviewed by 3 experienced stroke neurologists, assessing EIC (ASPECTS) and vascular signs (hyperdense middle cerebral artery stem and/or branches). Short-term outcome was assessed with the National Institute of Health Stroke Scale at 24 hours and long-term outcome with the modified Rankin Scale score after 3 months.Results: The prevalence of EIC was 54% and the agreement between assessors was good (kappa 0.52–0.67). EIC was independently associated with younger age and absence of diabetes mellitus. Neither EIC nor vascular signs were associated with 3-months outcome.Conclusions: ASPECTS is as simple, systematic approach to assessing EIC, and the interobserver agreement is good. Patient age and diabetes mellitus influence the presence of EIC.Keywords: acute stroke, computed tomography, ischemia, thrombolysi

Comparison between Ischemic Stroke Patients <50 Years and ≥50 Years Admitted to a Single Centre: The Bergen Stroke Study

Introduction. Young adults are likely to differ from old patients concerning cerebral infarction. Methods. We compared characteristics of patients aged under and above 50 years, admitted to the Department of Neurology with cerebral infarction between 2006 and 2009, based on prospective registration. Investigation followed one common protocol for both groups. Results and Discussion. One hundred patients (8.2%) were <50 years old, and the proportion of males was higher in this group (72% versus 55.8%, P = .002). Young stroke patients are more often current smokers (44.1% versus 23.6%, P < .001). Common causes for stroke in the young were cervical artery dissection (18% versus 0.6%, P < .001) and cardiac embolism due to disorders other than atrial arrhythmias (18% versus 5.5%, P < .001). Among the old, atrial fibrillation and flutter dominated (29.1% versus 5%, P < .001). Stroke severity and location did not differ. Old patients more often suffered from pneumonia (10.6% versus 2%, P < .003) and urinary tract infection (14.6% versus 2%, P = .001). Conclusions. Males dominate, and current smoking is more common in the young. Cervical artery dissection and nonarrhythmic heart disorders are frequent causes among young patients, while traditional risk factors dominate the old. Stroke severity is similar, but old patients seem more exposed for infectious complications

Magnetic and dielectric properties of polycrystalline Co0.5Ni0.5Fe2O4 materials prepared using mechanically alloyed nanoparticles.

Cobalt–nickel ferrite (Co0.5Ni0.5Fe2 O4) were prepared using a high energy milling and sintering. The starting raw materials of NiO, Co3O4 and Fe2O3 were subjected to 12 hr milling using a Spex8000D mixer/mill. The resulting material was molded into samples of toroidal/disc shape and subsequently sintered at various temperatures from 600 to 1000° C, at 100° C interval. The effect of sintering temperature on microstructure, saturation magnetization (Ms), and coercivity (Hc) was reported. The frequency dependence of the magnetic and dielectric properties such as permittivity, loss tangent, permeability and loss factor were investigated in the frequency range of 10 MHz–1.8 GHz. The results show that the real part of the permittivity at individual temperatures was constant within the measured frequency, while the loss tangent values decreased gradually with increasing frequency. The real permeability on the other hand remained fairly constant over certain frequency (around 1.0 GHz), and thereafter increases towards saturation thereby showing a good potential in the microwave frequencies region

Low Frequency AC Transmission - Investigating the Dynamics of an Export Cable for Offshore Wind Power Applications

In the following thesis, the properties of a 16 2/3 Hz, low frequency alternating current (LFAC) export cable was examined in both steady state and dynamic conditions, as part of a simplified offshore transmission system. Simulations were performed for both LFAC and conventional 50 Hz high voltage alternating current (HVAC) systems for comparison purposes. Introductory to the simulations, different cable models were investigated. Using MATLAB/SIMULINK SimPowerSystems, the use of the built-in distributed parameters model (DPM) was considered the best option for simulation, especially when studying the power cable in dynamic situations. For steady state conditions, the utilization of the series pi-model showed satisfying results, e.g. when the effect of voltage rise in a lightly loaded or unloaded transmission system was studied (Ferranti effect). The results revealed a significantly lower voltage increase across the LFAC cable compared to a conventional HVAC cable. Thus, in the case of sudden disconnections or loss of load, the risk of damaging transmission system components can be lower for an LFAC system compared to an HVAC system. Charging currents were observed to be lower and less sensitive to cable length variations for an LFAC cable compared to an HVAC cable. Thus, more active power is allowed to be transmitted in the LFAC cable. During energization of the cable, the LFAC voltages and currents experienced temporary transient distortions of the waveform before stabilizing at steady state, whereas the same distortions were not observed for the HVAC system. Transient distortions were also observed in the fault analysis for different short circuit (SC) events; three phase to ground, double phase to ground and phase to phase faults. The fourth SC event, the single phase to ground fault, showed very little distortion. However, the highest direct current (DC) offset magnitude was observed for the phase to ground voltages posterior to this fault. DC offsets were also observed after clearing the three phase to ground fault and double phase to ground fault, resulting from the lack of grounding in the cable system. The DC offsets were present for a long period of time; up to 100 seconds depending on the type of fault, and the magnitude of the DC offsets was significantly higher for the HVAC system. Connecting the cable's end terminal to ground through a shunt reactor resulted in a far lower DC offset magnitude which was rapidly damped to zero. Similar oscillations were observed for the HVAC system, and the DC offset was damped faster in this case due to higher resistance in the cable. The frequency of the oscillations were 30 Hz for the LFAC system and 44 Hz for the HVAC system, and it should be examined whether such oscillations may contribute to resonance in the power system. Possible measures to increase the damping of the oscillations would be a better optimization of the shunt reactor. Common for the dynamic situations investigated was the presence of harmonic distortion after switching operations or faults/clearing of faults. In the case of switching operations, the problem of transient distortion could possibly be more prominent for LFAC transmission systems compared to HVAC systems. However, further studies should be carried out before making final conclusions on this topic. In summary, the LFAC cable showed promising results in terms of overvoltages under steady and dynamic situations compared to a conventional HVAC system

Influence of sintering temperature on the structural, magnetic and dielectric properties of Ni0.8Zn0.2Fe2O4 synthesized by co-precipitation route.

The polycrystalline Ni–Zn ferrite powder with the chemical formula Ni0.8Zn0.2Fe2O4 has been synthesized using co-precipitation route. The toroidal and pellet form samples were sintered at various temperatures from 700 to 1300 °C/5 h in steps of 200 °C. The structures of samples were studied by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and the energy dispersive X-ray spectroscopy (EDXS). The magnetic and dielectric measurements were carried out using a vibrating sample magnetometer (VSM) and the impedance analyzer, respectively. The highest density of 4.48 g cm−3 was obtained for the sample sintered at 1300 °C. It was found that the initial permeability increased from 4 to 17 and the RLF was in the order of 10−3 to 10−4 in the frequency range of 1.0 MHz to 1.0 GHz. The dielectric constant and dielectric loss were lower compared to the reported values for conventional solid state technique. The electrical resistivity is in the order of 108 Ω cm. Therefore, low relative loss factor and high resistivity make these ferrites particularly useful as inductor and transformer materials for high frequency applications