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Electronic and Magnetic Properties of Manganites

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Chemical compounds called manganites have been studied for many years since the discovery of colossal magnetoresistance, a property that promises important applications in the fields of magnetic sensors, magnetic random access memories and spintronic devices. However, understanding -- and ultimately controlling -- this effect remains a challenge, because much about manganite physics is still not known. The pseudo-cubic perovskite series of oxides of type AMO3, where A is a divalent metal (or a rare earth) and M a transition metal, exhibit quite a wide range of magnetic and transport properties (depending on the elements A and M, as well as the doping). This, and their structural resemblance with the cuprates, has caused a revival of experimental and theoretical interest. Furthermore, many technical applications are appealing since thin films of these compounds can be grown relatively easily and there is much interest in using perovskite oxides for ferroelectric and superconducting applications. Almost all these compounds have a magnetically ordered ground state. However, the transition temperatures and the different types of order can vary considerably from one system to another. The peculiar transport properties, such as the colossal magnetoresistance (CMR) for the Mn based compounds are associated with a transition from a metallic ferromagnetic (FM) to an insulating anti-ferromagnetic (AF) or paramagnetic (PM) configuration. Sometimes this transition is accompanied by a structural distortion (as for Nd1-xSrxMnO3 or in La1-x Srx MnO3). In order to investigate the electronic and magnetic properties, we perform the first-principles calculations using the planewave self-consistent field (PWSCF) code based on density functional theory (DFT). Density functional theory is an approach for the description of ground state properties of metals, semiconductors, and insulators. The success of density functional theory (DFT) not only encompasses standard bulk materials, but also complex materials such as proteins and carbon nanotubes.

Keywords: Manganite, Density functional theory

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Low-Cost Electronic Nanodevices for High-Frequency Applications

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ÌýÌý Date: 20 October 2014(ex)

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A novel nanodevice, known as the self-switching diode (SSD), has recently shown promising properties as a room-temperature detector at terahertz frequencies. The SSD is a unipolar two-terminal device. It has a nonlinear current-voltage characteristic which resembles the behaviour of a conventional diode. The device therefore can be exploited as a rectifier. The planar structure of the SSD provides intrinsically low parasitic capacitance that enables signal rectification at higher speed than a standard vertical diode. It also allows the fabrication of a large number of SSDs in a single lithography step without the need for interconnection layers, which may introduce parasitic elements. Indeed, this is the key feature of the SSD that makes the whole fabrication process simpler, faster and at lower cost when compared with other conventional electronic nanodevices. Moreover, the SSD works very well with low-cost materials such as zinc oxide and organic thin films. This would be the center of my research with the aim of functioning SSDs at room temperature and at high speed using low-cost materials including graphene. The research will also explore the possible designs of novel planar diodes (other than SSD) that can be utilized as a high-speed rectifier. This will be performed using device simulation software such as ATLAS from Silvaco.

Keywords: Self-switching diode (SSD), low-cost materials, graphene

Mitigating Interference in a Heterogeneous Wireless Network using Channel Selection

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With the extensive development of heterogeneous wireless communication technology, combined with the advances of data acquisition, emerges a new trend of networked acquisition systems. Among this range of wireless technology, Wireless Sensor Networks (WSNs) has attracted much interest and visibility due to its huge application space. One challenge using the WSN is the short range of the sensor nodes that increases the complexity of transporting the data to a central server. The integration with Wireless Mesh Networks (WMNs) expands the communication range and allows mobility of the device. Thus, WSN can be used for forming the underlying sensing and WMN supports the network infrastructure in pervasive computing environments. However, interference is a problem as these networks share the same 2.4GHz industrial, scientific and medical (ISM) unlicensed band. The impact of the interference on the IEEE 802.11g (WMN) using OFDM modulation and on IEEE 802.15.4 (WSN) using DSSS is investigated in this research. Results from a series of experiments on the AIT wireless mesh campus network under realistic load conditions are presented. Packet retransmission and packets drop rate were measured and based on this knowledge, a channel interference classification (CIC) method is presented to identify the interfering operating channel. The method introduced is based on a technique proposed by Chowdhury et. al. for channel selection based on reference power values. This work modifies the technique to account for differences on channel spectrum characteristic found in tests on the Mesh Campus Network. A channel selection algorithm was then developed for WSN to decide on the operating transmission channel that is not under interference, hence reducing packet losses in the network. This paper will be of interest to network operators and organisations where critical information retrieval over wide area networks is required.

Keywords:ÌýWireless sensor networks (WSNs), IEEE 802.15.4, channel interference, wireless network coexistence.

This is due to its minute spaces and holes through which liquid and air may pass easily, without the need of the high-priced lithographic technique.

The characteristics of NPA (easily-controlled pore diameter, interpore distance and pore depth) form a befitting template for the synthesis of nanomaterials.

A well-ordered NPA can be employed through the fabrication of nanomaterials by template synthesis method, such as i) a two-step anodizing method and ii) pre-patterning method.

It is crucial to combine nanomaterials of uniform dimensions, as the properties of nanomaterials are significantly influenced by the dimensions.

However, the mentioned methods above are not feasible for large scale manufacturing due to the exorbitant cost and low throughput.

Hence, the objective of the study is to confirm on a simple method of oxide dissolution treatment to attain well-ordered NPA in shorter anodizing duration and higher temperature to enlarge the application on NPA in template synthesis of nanomaterials.

The study uses a single step anodizing at 50 V in 0.3 M oxalic acid at 15 degrees Celsius for 60 minutes, to produce NPA on aluminum surface.

By subjecting the nanoporous alumina to oxide dissolution treatment in a mixture of chromic acid and phosphoric acid, well-ordered pore and cell structure were obtained.

As a result, it was found that the oxide dissolution treatment improves the regularity of the cell and pore structure significantly and that this method is more convenient.

The post oxide dissolution treatment also exhibits ordered and nearly perfect hexagonal cell structure, a uniform closely honeycomb structure of NPA.

In addition, the pore diameters and the interpore distance are nearly uniform over the analyzed surface. Thus, the uniformity of the pore diameter and interpore distance are enhanced immensely.

Nowadays, wind energy is crucial for electricity companies as it is renewable and free resource. Malaysia has a good prospective in wind energy and have decided to opt for the wind energy to replace the fossil fuel which is non-renewable energy. Malaysia faces the four seasons such as southeast monsoon, northeast monsoon and two shorter periods of inter monsoon seasons. Hence, wind over in Malaysia is generally light with the speed less than 8 m/s.

The objective of this article is to analyse the performance of 300 Watts wind turbine to supply the energy for a power system. A wind turbine is instilled in front of Electrical Energy and Industrial Electronic System (EEIES) Research Cluster, Perlis. This small horizontal wind turbine manages to generate energy to charge the 600 Ah battery systems in the research lab and is pointed by a simple wind vane. Meanwhile, the maximum output voltage is 40V dc at the 5.54 m/s of wind speed.

Wind turbine is a rotating machine which converts the kinetic energy of wind into mechanical energy. When the wind flows past the turbine’s rotor blades, the blades turn and convert the wind energy into kinetic energy. This energy spins a rotor inside a generator and coverts into electrical energy. The more electrical energy generated the greater wind speed. Meanwhile, windmill is a machine that used mechanical energy. If mechanical energy is converted to electricity, the machine is called wind generator, wind turbine, wind power unit (WPU), wind energy converter (WEC), or aero generator.
Furthermore, Horizontal-axis wind turbines (HAWT) consists of motor raft and electrical generator which is must be pointed into the wind. It comprises a gearbox which turns the slow rotation of the blades into the speedy rotation that is suitable to drive an electrical generator. The turbine is constantly pointed upwind of the tower as a tower produces turbulence behind it.Ìý

It is essential to note that wind resource evaluation is a critical element in projecting turbine performance. Generally, annual average wind speeds of 5 m/s are required for grid-connected applications. Meanwhile, annual average wind speeds of 3 to 4 m/s may be adequate for non-connected electrical and mechanical applications.

The authors also added that Wind Power Density is a useful way to evaluate the resource available at the potential site. The wind power density reveals how much energy is available at the side by a wind turbine.Ìý

Nevertheless, the wind power is fluctuated as it will calm one day and howling the next. One of the most important tools in working with the wind, whether designing it or utilizing it, is a firm understanding of what factors that influent the power in the wind. The wind power could be classifies into two type which are Rotor Swept Area and Weibull Distribution.

In order to collect the data, the researcher utilized DAVIS Weather Station Vantage Pro2 (DWS) and Electrocoder. It manages to record the solar radiation, temperature, rain falls, wind speeds, wind direction, pressure and humidity. Speed and direction of the wind were measured by it which is installed at the top of the tower nearby the wind turbine. The Electrocoder is to measure the voltage where it records the data every second and manage to save the data for seven days. It will be downloaded once a week. The data on DWS and Electrocoder will be synchronizing to be recorded in every second.

From the data that have been collected, it has been proved that the wind speed is consistent at the specific time from 10.00 pm to 3.00 pm. Nevertheless, the wind fluctuates afterwards and at 3.00 pm, it drops. It starts to increase back at 4.00 pm until 10.00 pm. The maximum speed of wind blows is 6.22 m/s at the time of 6.39 pm and the maximum speed is 0 m/s at the time of 4.06 pm. This average value of the output voltage and wind speed has been recorded using the Electrocoder and DWS. The batteries merely can be charged after the wind turbine can produce voltage more than 12 Vdc systems.

In a nutshell, the performance of the wind turbine has been recorded and being analyzed by the authors. From the collected data, it has been proven that the wind turbine is reliable as it produced 40 Vdc at the speed of wind, 5.54 m/s have been recorded. Plus, it also has a good potential to meet the nominal power performance as specified by the manufacturer.

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Polymer Nanocomposites for Piping Application

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Epoxy based nanocomposites incorporating nanoclay and several types of geopolymer raw materials obtained from Saudi Arabia were explored for piping application. The flexural and compressive properties and performance were studied from several series of epoxy nanocomposites containing different ratio of epoxy/hardener, and nanoclay/geopolymer. In addition, different kinds of geopolymer raw materials such as fly ash, kaolin, pozzolonic, silica sand and white clay were employed as filler. The effect of different combination and ratio of these materials on the mechanical properties and morphology of the resulted nanocomposites were investigated. Preliminary studies showed promising properties of these nanocomposites for further development in pipe application.

Keywords:Polymer, Nanocomposite, Nanoclay, Geopolymer, Pipe, compressive strength, flexural strength, flexural modulus.

One potential renewable energy source that has been developed rapidly since the late 1970s is wind power, which is generated through the creation of wind turbines. Capable of Ò¹÷ÈÖ±²¥ clean energy, without needing any fuel transport that are harmful to the environment, the wind, along with the sun and running water, are all sources of renewable energy. This is in contrast to coal, oil and gas, which rely on fossil fuels from mines or oil and gas fields that will one day run out of supply.Ìý

Modern wind turbines are efficient, reliable and produce power at reasonable cost. As such, it has created a market for renewable energy as well as development in research. One of the developments is the technology in wind turbine. The control system have become cheaper and more advanced, new rotor blades which can extract more power from the wind were created, and the invention of new power electronic equipment makes it possible to use variable speed and to optimize the capacity of the turbines. In just a few decades, wind power has developed into a fast growing industry which no longer needs subsidies and is able to manufactures wind turbines that produce power at competitive cost.Ìý

This paper plans to show the principle of work of vertical axis turbines, which is one of the several types of wind turbines available on the market, as well as to evaluate the potential of wind energy in Perlis.Ìý

The energy conversion process of wind energy using wind turbines includes the rotation of blades that convert the wind energy into rotational mechanical energy on the shaft and to an electric generator. There are several different design concepts for wind turbines. One basic classification is the Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). Vertical axis wind turbines are a type of turbine where the main rotor shaft runs vertically. The advantages of VAWT compared to the horizontal axis type of turbine are its simple construction, the lack of necessity of over speed control, the acceptance of wind from all directions, the limitation in mechanical design due to the control system and the electric generators that are set up statically on the ground.Ìý

In general, there are two distinctive types of VAWT, namely the Darrieus and Savonius types. For the Darrieus, there are three common blades which are Squirrel Cage Darrieus, H-Darrieus and Egg Beater Darrieus. The speed of wind speed for this paper is modeled using the Weilbull distribution.

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Another aspect of wind energy that this paper is looking into is the potential of utilizing wind turbines in the state of Perlis. According to Malaysian Meteorological Department, wind over this country is generally light with some periodic changes.

There are four seasons in Malaysia, namely the southwest monsoon, northeast monsoon, and two shorter period of intermoonsoon season. But, in Perlis, due to its close proximity to Thailand, the tendency is to the tropical monsoon season. The month of April, 2011 was chosen as the period of study for this paper.

The conclusion garnered from this paper is that the state of Perlis has the potential in developing the wind energy system. On the other hand, through the recording data from the use of vertical axis wind turbines, the results shows that this type of wind turbine is the most suitable to be used in Perlis as the wind speed in this state is low.

In fact, automatic analysis of medical cell images is becoming more important in pharmacology and toxicology research. According to Rashid and his team, an automated analysis system would produce a more standardised automatic image analysis, which would conquer the current limitation of manual detection system. In addition, images will be mathematically defined with greater precision compared to the earlier images processing techniques. Thus, this would enhance and accelerate the analysis of image processing with high precision.

Rashid and his team chose to focus and review on some of the general segmentation and classification methods for red blood cell images, which are blood cells counting and segmentation of red blood cells. Blood count helps in detecting many diseases in early stage, whereas, segmentation helps in anaysing diseases and performing complete blood count (CBC) efficiently and it is cost effective.

Some of the recent types of methods in segmentation shared are:

1. Thresholding -based on histogram characteristics of pixel intensities of image.Ìý
2. Morphological Operation –continuity-based techniques which involve the processing of shapes, to segment the red blood cell images
3. Colour Image Segmentation –allow more reliable image segmentation than greyscale images and applying of hue feature.Ìý
4. Model-based contour tracing –to overcome the problem of automatically segmenting a Scanning Electron Microscope image of red blood cells that have high number of overlapping cells and relatively smooth contour.Ìý
5. Tabu Search –a method for finding elliptical cell boundaries.
6. Matlab –to overcome the problem of counting overlapping red blood cells by applying new algorithm by using the method.
7. Fluorescent Microscopy Images –can remove object with poor contrast and distance transformed watershed segmentation.

Some of the recent types of methods in classification shared are:

1. Multilayer Perceptron –classifying various types of blood cells.
2. Support Vector Machine –analyses data and recognize patterns which could be used for classification and regression analysis.Ìý
3. Learning Vector Quantization –a type of artificial neural network and can be applied to multi-classification problem is a natural way. E.g. in classifying blood cells and bone marrow

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Plastic units are not suited for rough handling which is crucial for all storage equipment to bear. Durability and impact resistance are the two most important things that we would not have to bother with metal units, causing industries and researchers to feel obliged to find an accurate calculation to increase the productivity rate during the metal cutting processes to optimize productivity.

Due to the increasing demands, researchers from UniMAP have taken initiative to find out the precise calculation to increase the productivity rate of the metal cutting machine. It is known that the strength of the machine operating modes reflects on the intensive wear of machine tool cutters to increase the dynamic forces, speed of the cutting process, and magnitudes of feed rates and the depth of cut.

The most unreliable elements, and yet one of the most important in a machining tools is the metal cutter itself. Comparing it to other components of machining tools such as spindles, bearings and sliders they are many times more reliable than metal cutters.

As a result, machine tools have to go through many cutters or blade replacement processes that ultimately affecting productivity and cost. However, the manufacturing industries are left clueless in between the processes as they are not able to estimates precisely the productivity rates due to the absence of the specific mathematical dependency.

However, researchers A.M. Ahmed Alwaise, R. Usubamatov and Z.M. Zain managed to come up with a mathematical equation to determine the productivity rate of an automatic machine tool on the change of processing mode.

The equation considers all the major aspects in calculating the productivity rate such as the total machine working time as in when it produces products as well as the time losses due to the failures of cutters, replacement, repairing and tuning.

The proposed equation of the productivity rate for automatic machine tool is a function of cutting speed and parameters of tool life, which enables calculations at the pre-stage of preparing economically effective manufacturing processes for products.

This finding enables industries to find the optimal processing mode that can give the maximum productivity rate of a machine tool.Ìý