Geometry Optimization of Two Infinite Parallel Plates with Free Convection Heat Transfer

In this study, geometrical optimization of two infinitive plates for the enhancement of heat transfer between the plates is investigated by considering free convection and thermal radiation as heat transfer mechanisms. It is assumed that heat sources with specified length are placed in a linear array with infinitive length on the lower plate. These heat sources are placed at a specified distance between them. Heat flux of the heat sources and the temperature of the upper cold plate are the given data, and the mean temperature of the heat sources, the temperature difference between the upper cold plate and the mean temperature of the heat sources and the Nusselt number are the major parameters for optimizing the geometry of the plates. First, the problem is solved for two familiar geometries: when there exists an upper plate and when it is omitted. Eventually, a situation in which there are vents in the lower and the upper plate is investigated, and the optimum position of these vents as well as their sizes are obtained. The results show that placing vents on the plates can be very effective for enhancing heat transfer from the heat sources. For a particular array of heat sources and vents on the plates, the Nusselt number has the highest magnitude in comparison with other geometries, and consequently, the maximum heat transfer is available

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

The study of the lightning interaction with tall strike objects has attracted considerable attention of lightning researchers lately. Many lightning measurements including current and associated electromagnetic fields were recently made all over the globe namely in Russia, South Africa, Germany, Brazil, Japan, and Austria. It is a novel area of studies, and the resolution of associated questions will have an impact upon many lightning-related applications such as lightning protection and the determination of lightning parameters from remote field measurements. The main objective of the thesis is to carry out further theoretical investigations and experimental measurements to understand and elucidate recently raised questions on the characteristics of lightning return-strokes to tall structures and their associated electromagnetic radiation. Chapter 2 presents a review on recent progress in the modeling of lightning strikes to tall towers and associated experimental data obtained during the last decade or so. Two types of return stroke models namely the Engineering Models, and the Electromagnetic or Antenna-Theory (AT) models, extended to take into account the presence of a tall strike object are discussed. The Chapter contains also a description of the computational methods for the evaluation of electromagnetic fields generated by a lightning strike to a tall structure, as well as an overview of available data on lightning current and associated electromagnetic fields. The chapter finally highlights some important questions raised by different research groups in the past few years which call for further investigations. These questions are as follows: No systematic theoretical analysis nor experimental data are available for electromagnetic fields in the immediate vicinity of a tall structure struck by lightning. The characterization of nearby electromagnetic fields is particularly important in the analysis of the interaction to nearby electrical and electronics systems. Why do lightning return stroke models not reproduce the far-field zero crossing associated with lightning to tall structures? How should these models be revised to be able to reproduce such an effect? How should the engineering models be revised in order to remove the associated current discontinuity at the return stroke wavefront? It is well-known that the measurements of electromagnetic fields from lightning are affected by the presence of nearby buildings and metallic structures. However, no systematic and quantitative analysis of such an effect is presently available in the literature. The work presented in this thesis addresses all of the above questions. The main original contributions of this thesis, consisting of both theoretical and experimental work, are presented in Chapters 3 through 6. Chapter 3 is devoted to a theoretical description of the signature of electric and magnetic fields at very close distance associated with lightning strikes to a tower. It is shown that the electric field generated by a lightning return stroke to a tall structure can change polarity at very close distance range. This change in the polarity seems to be a specific signature of the very close vertical electric field. A simple equation is derived which provides an estimate of the critical distance below which such an inversion of polarity might occur. It is also shown that the inversion of polarity depends on the value of the reflection coefficient at the base of the tower and disappears for reflection coefficients close to 1. On the other hand, other parameters such as the return stroke speed, the reflection coefficient at the top of the strike object, and the adopted return stroke model seem not to have an impact on the inversion of polarity. Simulation results also showed that the electric field peak at distances beyond the height of the tower or so exhibits the typical 1/r dependence. At closer distances, however, the E-field peak features a saturation, due to the so-called tower shadowing effect. This shadowing effect results in a substantial decrease of the nearby electric field. On the other hand, the magnetic field peak varies inversely proportional to the horizontal distance and does not depend significantly on the presence of an elevated strike object. Chapter 4 introduces an improved version of the engineering models for return-strokes to tall structures which accounts for (1) the presence of possible reflections at the return stroke wavefront, and, (2) a return stroke initiation above the structure due to an upward connecting leader. We also propose an elegant iterative solution that can be easily implemented into computer simulation programs to take into account in a straightforward way multiple reflections occurring at the discontinuities at the tower ends and at the return stroke wavefront. Simulation results for the magnetic fields are compared with experimental waveforms associated with lightning strikes to the CN Tower (553 m). It is shown that taking into account the reflections at the return-stroke wavefront results in better reproducing the fine structure of the magnetic field waveforms. Chapter 5 presents and discusses obtained measurements of electric (vertical and radial) and magnetic fields from leaders and return strokes associated with lightning strikes to the Gaisberg tower in Austria obtained in 2007 and 2008. The data include simultaneous records of vertical and radial electric fields, which were obtained for the first time at such close distances. It is found that the vertical and radial electric field waveforms appear as asymmetrical V-shaped pulses. For the vertical electric field, the initial, relatively slow, negative electric field change is due to the downward leader and the following fast positive field change is due to the upward return stroke phase of the lightning discharge. For the horizontal electric fields, however, the bottom of the V is not associated with the transition from the leader to the return stroke. The horizontal field change due to the return stroke is characterized by a short negative pulse of the order of one microsecond or so, starting with a fast negative excursion followed by a positive one. In addition, an analytical expression for the radial electric field, assuming a uniform charge distribution along the leader with constant speed is derived. It is also shown that the return-stroke vertical electric field changes appear to be significantly smaller than similar measurements obtained using triggered lightning. This finding confirms the shadowing effect of the tower predicted by the theoretical analysis of Chapter 3, which results in a significant decrease of the electric field at distances of about the height of the tower or less. Finally, the ability of two different models for the return stroke in reproducing measured vertical and horizontal electric fields is tested using the obtained measured data. The considered models are (1) the engineering MTLE (Modified Transmission Line with Exponential Decay) model, and (2) the electromagnetic model implemented using the Numerical Electromagnetics Code NEC-4. It is shown that both models predict electric field waveforms which are in reasonable agreement with measured waveforms. In general, the predicted fields by the electromagnetic model appear to be in better agreement with measured data, because of the direct use of the measured current waveform as an input and the more accurate representation of the tower. Chapter 6 reports on the effect of nearby buildings on electromagnetic fields from lightning. Indeed, sensors used for the measurement of lightning electric and magnetic fields are often placed close to or on top of buildings or other structures. Metallic beams and other conducting parts in those structures may cause enhancement or attenuation effects on the measured fields. Experimental waveforms radiated from distant natural lightning recorded during the summers of 2006 and 2007 are presented. Electric and magnetic field waveforms were measured simultaneously on the roof of a building and on the ground at different distances away from it. The results suggest that the measured electric field on the roof of the building could be enhanced by a factor of 1.7 to 1.9, whereas the electric fields on the ground experienced a significant reduction by a factor ranging from 5 to 20. Also, it is shown that for a sensor located on the ground close to a building, the magnetic field component perpendicular to the building can experience significant attenuation, presumably due to the effect of the induced currents in the building. The magnetic field on the roof of the building seems not to be significantly affected by the building. Simulations using the Numerical Electromagnetic Code (NEC-4) were also carried out in which the building was represented using a simple wire-grid model. The simulation results support in essence the findings of the experimental analysis, despite quantitative differences which are ascribed, at least in part, to the oversimplified model of the building

The Effect of Wetting and Drying Cycles on Selected Physical Indicators of Biochar- and Rockwool-Based Growth Media

IntroductionMonitoring the changes in physical and hydraulic properties and stability of growth media due to root growth effects and wetting and drying cycles is important. Wetting and drying cycles can probably change physical characteristics, availability of water, air and nutrients for the plant and, as a result, might affect the growth and yield of the greenhouse plants. The growth period greatly affects the physical characteristics of the growth substrates; therefore, the watering of growth substrates should be managed according to these changes to avoid improper irrigation.Materials and MethodsIn this study, 14 growth media were prepared from individual substrates with different volumetric ratios. In order to evaluate the changes of growth media over the time (i.e., during consecutive irrigation events) in the greenhouse, 10 wetting and drying cycles were applied on the growth media in the lab. Several physical indicators including easily available water (EAW), air after irrigation (AIR), water buffering capacity (WBC) and water holding capacity (WHC) of the growth media were determined before and after the wetting and drying cycles. Besides, the subsidence, decrease of mass and decomposition of the growth media were determined over the time. Total porosity (TP), bulk density (BD), particle density (PD), pH and electrical conductivity of the mixtures were measured as well.Results and DiscussionThe pH values in the growth media varied from 5.72 to 6.94. The maximum pH value was related to sawdust- sugarcane bagasse biochar produced at 300◦C vermiculite-zeolite, and wheat straw-vermiculite substrates, and the minimum value was related to the cocopeat-perlite substrate. The values of EC in the growth media varied from 0.21 to 1.43 dS m-1. The highest and lowest EC values among the growth substrates were related to date palm bunches-vermiculite-rockwool and rockwool (0.2)-perlite substrates, respectively. The bulk density (BD) values of the growth media varied in the range of 0.163-0.401 Mg m-3. The values ​​of total porosity (TP) of the growth media varied in the range of 64.8-82.8%v/v. The highest TP was related to the cocopeat-perlite substrate. The TP values ​​of most of the substrates were greater than 70%v/v. The average values of EAW in the growth substrates ranged from 0.123 to 0.272 cm3 cm-3. The highest EAW was related to the sawdust-sawdust biochar produced at 500 ◦C vermiculite-zeolite substrate. The application of wetting and drying cycles increased EAW in most of the growth media. Therefore, it can be stated that the time had a positive effect on the EAW in most of the growth media. The average values of AIR before and after the application of wetting and drying cycles for the growth media varied in the range of 0.063-0.240 cm-3 cm3. The highest value of this indicator was observed in the sawdust-date palm bunches biochar produced at 300◦C vermiculite substrate. In all substrates (with the exception of the sawdust-sawdust biochar produced at 500◦C vermiculite-zeolite), the AIR increased after wetting and drying cycles. The range of WHC values before and after applying wetting and drying cycles was 0.453-0.699 cm3 cm-3. The highest WHC belonged to the wheat straw-vermiculite substrate. The WHC values of five growth media, including cocopeat-perlite, decreased due to the application of wetting and drying cycles, and the WHC values of nine growth media decreased. The most stable substrate after the wetting and drying cycles was rockwool-sawdust-vermiculite. The effect of time on the quantity of WBC was positive, so that with the application of wetting and drying cycles, the WBC values of most of the substrates increased. In all substrates, subsidence and dry weight reduction were observed after the wetting and drying cycles. These changes were low for the substrates with a high volumetric ratio of inorganic materials. The least change among the growth substrates in terms of decomposition (dry weight reduction) was related to the completely inorganic substrate rockwool (0.1)-perlite (%0.17). The most stable substrate in terms of subsidence after wetting and drying cycles was the rockwool-sawdust-vermiculite, which has a large volumetric ratio of individual inorganic substrates. The highest subsidence was observed in the substrates containing wheat straw (wheat straw-vermiculite and date palm bunches biochar produced at 300◦C wheat straw-vermiculite). The organic matter content in all the growth substrates decreased over time (after wetting and drying cycles). The decrease of organic matter in the substrates can be related to the decomposition of organic materials as a result of wetting and drying cycles.ConclusionThe BD, TP, EAW and WHC of the majority of growth media were in the optimal ranges and for some mixtures even better than cocopeat-perlite. Wetting and drying cycles could affect the growth media through several processes such as decomposition of organic compounds, displacement and rearrangement of particles, fragmentation of particles, shrinkage, hardening and subsidence. The growth media with a high percent of organic substrates were unstable as compared with those containing a high proportion of inorganic substrates. In general, the wetting and drying cycles increased the frequency of micropores in the growth media. The wetting and drying cycles positively affected EAW, WHC, AIR and WBC of most growth media. These findings imply that wetting and drying cycles may improve the growth media according to the studied extensive variables. However, it is necessary to study the intensive variables such as hydraulic conductivity, oxygen diffusion and pore tortuosity in the growth media for better evaluation of the impact of wetting and drying cycles as well

Potential promising anticancer applications of β-glucans: a review

β-Glucans are valuable functional polysaccharides distributed in nature, especially in the cell walls of fungi, yeasts, bacteria, and cereals. The unique features of β-glucans, such as water solubility, viscosity, molecular weight, and so on, have rendered them to be broadly applied in various food systems as well as in medicine to improve human health. Moreover, inhibition of cancer development could be achieved by an increase in immune system activity via β-glucans. β-glucans, which are part of a class of naturally occurring substances known as biological response modifiers (BRMs), have also shown evidence of being anti-tumorogenic, anti-cytotoxic, and anti-mutagenic. These properties make them attractive candidates for use as pharmaceutical health promoters. Along these lines, they could activate particular proteins or receptors, like lactosylceramide (LacCer), Dickin-1, complement receptor 3 (CR3), scavenge receptors (SR), and the toll-like receptor (TLR). This would cause the release of cytokines, which would then activate other antitumor immune cells, like macrophages stimulating neutrophils and monocytes. These cells are biased toward pro-inflammatory cytokine synthesis and phagocytosis enhancing the elicited immunological responses. So, to consider the importance of β-glucans, the present review introduces the structure characteristics, biological activity, and antitumor functions of fungal β-glucans, as well as their application

Fatigue in multiple sclerosis is a diagnostic challenge: A cross-sectional study

Introduction: Multiple sclerosis (MS) is a chronic and unpredictable demyelinating disease of the central nervous system (CNS). While MS is mostly known for muscle weakness, numbness, and pain, but fatigue is the most common complaint of this condition. Despite this fact, MS related fatigue is one of the most misunderstood symptoms. Methods: A non-interventional study of 100 individuals was conducted in the MS clinic, Tabriz University of Medical Sciences. Patients were divided into groups with and without complaints of fatigue. The course of the disease was determined for all patients. To quantify fatigue, the Modified Fatigue Impact Scale (MFIS) was used. Furthermore, mood disorders, pain, disability, nocturia, insomnia, and spasticity were evaluated among the patients. Results: Overall, fatigue was diagnosed in 61 through 100 patients. Depression was reported in 23 patients of whom 19 had fatigue (P=0.015). 40 patients showed anxiety 33 of which had fatigue (P>0.001). 53 patients of whom reported to have pain (76 patients) showed fatigue (P=0.001). Insomnia was reported in 27 patients, where 21 of them had fatigue (P=0.036). Nocturia was reported in 10 patients, of whom 9 had fatigue (P=0.047). Spasticity was detected in 9 patients, all of whom had fatigue (P=0.012). Conclusion: There are several factors directly and indirectly associated with fatigue that are either fatigue-induced, caused by fatigue, or showing a two-way relationship with it. Understanding these links and attempting to reduce them will improve the quality of life for these patients