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Resistivity of Nanocrystals




Hasan Abu Kassim. Norhasliza Yusof and Keshav N. Shrivastava



Department of Physics, University of Malaya, Kuala Lumpur 50603, Malaysia

We find that the usual temperature dependence of the resistivity is considerably modified in going from crystals to nanocrystals. The usual T 5 dependence is completely changed to the exponential of negative inverse temperature. The quantized resistivity of h/2e2, because of two electrons travelling in opposite directions, acquires temperature dependence and the value for four electrons, h/4e2, is also expected to appear. The experimental data of resistivity of nanometer size Ag crystals has been examined and found to be in agreement with the theory. The experimental data of single-walled carbon nanotubes has also been examined to find how it depends on the length when tube diameter is very small compared with the length. It is found that electrons are scattered along the cylindrical length due to oscillations (phonons) in the tube. In the case of a thin nanocrystal the electrons exhibit flux quantization. Although the phenomenon of flux quantization is usually discussed in the superconductors, it does not require superconductivity. The single electrons can exhibit flux quantization with unit charge as e and pairing with charge 2e is not necessary. In some experiments, two electrons travel in opposite directions so that the unit charge 2e appears without superconductivity.



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Improvement of Power Output by Selecting the Appropriate Material under Various Conditions
Javed Samia and M. A. K. Lodhib
a Department of Space Science, University of The Punjab, Lahore, Pakistan

b Department of Physics, Texas Tech University, Lubbock, TX 79409, USA

Alkali metal thermal to electric converter (AMTEC) is device that converts the thermal energy into electrical energy. Basically, it consists of two major parts electrolyte and electrodes. Beta alumina ((// Alumina) solid electrolytes (BASE) is used as electrolyte and materials like Molybdenum (M0), titanium-nitride (TIN) rhodium-tungsten (RhW), Platinum-tungsten (PtW) etc. are used for electrodes.

Life’s time of electrode is defined as the time required to grow the grains of electrode to a diameter of 1 m . During operation of AMTEC electrode and keeping the efficiency higher it is necessary grain growth should be minimal. The smaller grains combine with together to produce large grains and large grains combine with large grains and produces another grain of large diameter. As a result area spacing between the grains open and total grains decreases. The surface contact among the electrode grain reduces. This in turn affect the power output pf AMTEC. In this work we present the power dependence on the grain growth model parameters and look for the parameters of AMTEC power output and its electrode materials.

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Single Electron Transistor Structure Characterization Using Scanning Probe Microscopy
U. Hashim1, Sutikno2, Z.A.Z. Jamal3 and Y. Wahab4
1,2,3 School of Microelectronic Engineering

Universiti Malaysia Perlis

4Physics Department, Faculty of Sciences

Universiti Teknologi Malaysia

Single electron transistor is able to be fabricated through either top down or bottom up method. Top down fabricated single electron transistors have still been attracting a lot of interests of many researchers at recent years. Most essential steps in top down fabrication of single electron transistors such as nano structure etching and pattern dependent oxidation for nano structure shrinking. Both those steps need surface morphology characterization and profile analysis. Three dimensions profile analysis of nano structures is characterized by scanning probe microscopy. Variations of etching time ranges from 55 s to 85 s and oxygen flow rate of 10 sccm up to 50 sccm are made to control nano structure dimensions such as height, width, distance and gradient. Such controllable dimensions are to provide established single electron transistor fabrication.




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Earth’s Atmosphere Link to Solar Activity
Jahanzeb Qureshi a, Benjamin Noll b and M.A.K.Lodhi a,b
aDepartment of Space Science, University of The Punjab, Lahore, Pakistan

bDepartment of Physics, Texas Tech University, Lubbock TX 79409 USA.

The solar activity in the form of appearance of sunspots on its surface varies periodically on average of eleven year cycle. As a consequence of this activity or independently there are other solar phenomenon which vary with the same periodicity for example, the emission of radio waves, ultraviolet, X-rays and high energy particles increases substantially during the solar maximum. However, the total solar luminosity barely increases (0.1%) from solar minimum to solar maximum. If solar activity does affect the Earth’s climate, it must be through some very subtle mechanism. Perhaps the expansion of the Earth’s atmosphere with solar maximum may somehow cause changes in the Earth’s weather. In this paper the effect of solar activity studied on the air density of Earth’s upper atmosphere is presented. The Earth’s atmospheric density fluctuates by far more during the maximum solar activity than what it is during the minimum solar activity on monthly and daily basis.




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EM Wave Scattering from an Infinitely Long Cylinder
Ithnin Abdul Jalila and Rio Hirowati Sharifudinb
aDepartment of Physics and bInstitute of Mathematical Sciences

University of Malaya, 50603 Kuala Lumpur, Malaysia

The scattering of electromagnetic(EM) plane waves, with TM and TE modes, from an infinitely long cylinder has been considered. We used the T-matrix method and the repetitive summation of the partial waves, Bessel and Hankel functions have been performed computationally. The quantities of interest calculated are the scattering coefficients, extinction and scattering cross-sections and the Mueller scattering matrix. We studied the variation of the quantities with the radius, refractive index and the tilt angle of the cylider.



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Affective Computing on Mathematics Learning
Panimalar a/p Manoharan, Geraldine David
Faculty of Information and Technology

Multimedia University (Malacca Campus),75450 Ayer Keroh

Melaka

Mathematics as a subject has remained mysteriously difficult and unpopular for most university students. This is despite the fact that no one is in doubt of its importance in almost all careers, especially in the science and technological fields. Studies have shown that students that have positive attitude toward mathematics tend to do well in the subject, and students that have negative attitude toward mathematics tend to perform badly in the subject As a result, intensive research has been done to determine students’ attitude towards mathematics in relation to different variables. The method used to develop this system is a combination between 3D system model, affective computing and three important topics in mathematics, to show the differences to learn mathematics in a very easy way & user friendly manner as well as it will enhance the use of the Multimedia Learning System (MMLS) used by students of Multimedia University (MMU). This way might increase interest among students to learn mathematics because the system is using emotions and 3D system which is totally a different way to learn using computer. This 3D system is another solution that will make mathematics an easier subject to learn because graphs can be plotted in one coordinate system using different colors and lighting conditions. Besides that the system can plot high quality equation and table based graphs, zoom them, rotate, view at any angle and even animate. All types of coordinates are supported for example Cartesian, cylindrical, spherical and many more.



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Thermal Symmetry of Markovian Master Equation
B. A. Tay
Department of Physics, University Putra Malaysia, 43300 UPM Serdang, Selangor, Malaysia.

The Markovian quantum master equation of the reduced dynamics of a harmonic oscillator coupled to a thermal reservoir is shown to possess a thermal symmetry. This symmetry is a Bogoliubov transformation that can be represented by a hyperbolic rotation acting in the Liouville space of the reduced dynamics. The Liouville space is obtained as an extension from the Hilbert space by introducing tilde variables as carried out in thermo¯eld dynamics formalism. The angle of rotation depends on the temperature of the reservoir, or the value of Planck's constant. The symmetry connects the thermal states of the system between any temperature, including absolute zero that contains a purely quantum effect, or between any value of Planck's constant.



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Si and SiGe Based Materials for Microelectronic and Photonics Applications
Md Roslan Hashim
Nano-Optoelectronics Research Lab, School of Physics, Universiti Sains Malaysia 11800, Penang

Research in Si/SiGe for microelectronic and photonic applications is spurred by the idea of realizing the integration of both photonic and electronic systems on a single chip. The technology is about manipulation of the low cost and matured silicon technology while enjoying the benefits of bandgap engineering to improve performance due to the inclusion of germanium into the silicon. In microelectronic applications, silicon based technology has been in the market for more than 60 years. The technology has matured itself to the extent that the low cost of production is always the main advantage over other technologies. However Si only technology suffers from low operation frequency compared with GaAs technology. With the introduction of a small percentage of Ge into Si, the resulting SiGe devices can compete with GaAs technology in terms of device performance and at the same time benefit from the low production cost of Si technology. With the maturity of Si based technology in microelectronic applications, any new development on Si and SiGe for photonic applications will hold the promise of realizing integrated optoelectronics on the same wafer. This paper will discuss some developments in Si and SiGe based materials for optoelectronics applications especially in our research lab. This will include fabrication and simulation works on Si/SiGe transistors, Si/SiGe photodetector, Si/SiGe waveguides and porous silicon.



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Thermal Diffusivity Determination of CuSe Metal Chalcogenide Semiconductor Using Photoacoustic and Photoflash Technique

L.Y.C. Josephinea, Z.A. Talibb, W.M.M. Yunusb, Z, Zainalc, W.D.W. Yusoffb, and M.M. Moksinb
a Universiti Pertahanan Nasional Malaysia, Kem Sungai Besi, 57000 Kuala Lumpur.

bDepartment of Physics, Universiti Putra Malaysia, 43400 UPM, Serdang.

c Department of Chemistry, Universiti Putra Malaysia, 43400 UPM, Serdang.

Copper selenide (CuSe) is an interesting semiconductor compound with various applications in solar cells, super ionic conductors, photo-detectors, photovoltaic cells and Shottky-diodes. Our current research efforts are directed towards an investigation concerning how to determine the thermal diffusivity value of the CuSe metal chalcogenide semiconductor using the photoacoustic and photoflash technique. The thermal diffusivity of CuSe was determined to be at 1.125 x 10-2 cm2/s with sample thickness in the range of 0.0921 cm to 0.3445 cm using photoflash technique. The thermal diffusivity obtained from photoacoustic phase fitting technique is 1.126 x 10-2 cm2/s with sample thickness in the range of 0.0456 cm - 0.1064 cm. Both techniques show the thermal diffusivity value yielded good agreement with each other with the experimental error within  0.1%. The measured results have shown that the thermal diffusivity value can be obtained independent of the sample thickness. Our studies validates that the photoacoustic techniques is particularly suitable for the measurements of sample thickness lower than 1 mm while the photoflash technique is suitable for the sample thickness higher the 1 mm. The PA technique has shown more attractive features as compare to the photoflash technique. It has been proved to be more convenient, reliable and the sample size required is very small for thermal diffusivity measurement. In the case of semiconductors, the photoacoustic signal will provides us the information regarding the carrier-transport properties besides the thermal parameters.



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The Thermoluminescence Response of Ge-Doped Optical Fibres To X-Ray Photon Irradiation
Suhairul Hashim a, Ahmad Termizi Ramlia, D.A. Bradley b and Husin Wagirana
a Department of Physics, Universiti Teknologi Malaysia, 81310 Skudai, Johor Darul Takzim, Malaysia

b Department of Physics, University of Surrey, Guildford, GU2 7XH, U.K.

Thermoluminescence dosimetry (TLD) is useful in medical application to determine dose received by patient in cancer treatment. The interest is to introduce optical fibres as a new thermoluminescence (TL) material. This paper presents preliminary results on the TL response reproducibility with various doses and fading of Ge-doped optical fibres to X-ray photon irradiation. The optical fibres investigated were typical single-mode fibres, with a core diameter of 130 µm. Prior to X-ray photon irradiation, the calibration of diagnostic X-ray machine doses was made using ionization chamber. Dose rate of 58.31 mGy/s was delivered to the Ge-doped optical fibre using 49.8 kVp and 986µA current setting. During irradiation, a retort stand was used to hold the plastic container in order to get uniform exposure. TL response of Ge-doped optical fibre following X-ray irradiations was found to be linear in medical radiotheraphy dose range up to 10 Gy. In fading studies, a total of 30 samples of Ge-doped optical fibres were simultaneously irradiated, first to 2 Gy of X-rays and then subsequently to 10 Gy of X-ray dose. The performance of Ge-doped optical fibres was then compared against the currently available TL material i.e. TLD-700 (LiF:Mg,Ti). The average reading from five repeated measurements on both types of TL material were recorded on a daily basis over a period of six days. After irradiation, and until readout, the samples were kept in the lightproof container at a room temperature. Six days after irradiation, the Ge-doped optical fibre exposed to 2 Gy showed a 26.2 % loss of signal compared to the yield obtained 24 hours after irradiation, while at 10 Gy the fibre showed a loss of 19.7 %. Conversely, for TLD-700 the respective values were 75.9 % and 36.1 %.



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Generation of QSAR Models for Cancer Treatment and Its

Application to Grouping the Photosensitizer Agents

Sharifuddin M. Zain, Noorsaadah Abdul Rahman, Neni Frimayanti


Department of Chemistry, Faculty of Science, University of Malaya

50603 Lembah Pantai, Kuala Lumpur Malaysia

Photodynamic therapy (PDT) sometimes referred to as photo chemotherapy is widely used as a curative and palliative treatment for a variety of solid malignancies. PDT involves the action of a drug by visible light, resulting in the generation of cytotoxic oxygen species. In this study, Quantitative Structure Activity Relationship (QSAR) has been used to develop a model that can correlate the features of chemical compounds (photosensitizer) with their activity (i.e. inhibition concentration). The models were constructed by first generating a series of descriptors from three dimensional representations of the compounds in the data set. In this study, data set consists of 36 compounds were then divided to a training set (24 compounds) for QSAR model development and a prediction set (12 compounds) for model validation. Multiple linear regression analysis (MLRA) has been used to generate the model. The best QSAR model has r2 value of 0.7246 and r2 (CV) value of 0.6419, thus low predictive power. Removing some outliers (i.e. high residual value) was needed to improve the model. A new model with r2 value of 0.8697 and r2 (CV) value of 0.7080 was generated. This model is capable of predicting the inhibition concentration (IC50) value of the excluded 12 compounds in the prediction set with r2 value of 0.70. The Euclidean distance concept was applied to measure the similarity between active compounds in the data set with the external set by using a set of descriptors in the QSAR models. The validation of QSAR models were also carried out in a cluster analysis. It can also be used for grouping the compounds base on their main properties in the QSAR models.


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Conductivity and Dielectric Studies of a Polyvinyl Alcohol Lended with Zeolite – Technology in Membrane Fuel for Direct Methanol Fuel Cell (DMFC)
Sharifah Zuraiha S.M.Zain 1, Elias Saion 1, Muhammad Zaki A.R.2
Physics Department 1, Chemistry Department 2

Faculty of Science, Universiti Putra Malaysia,

43400 Serdang, Selangor D.E.

Direct methanol fuel cell (DMFC) has a strong potential to be a future source of electrical energy and equally capable to handle its multiple stationary and mobile applications. The key component in DMFC is its solid polymer electrolyte membrane (PEM) and when DMFC works, PEM conducts protons. Nafion® at present is the sole membrane among all other commercially available proton conducting membranes that has the best proton conductivity but when used in DMFC, along with proton conduction, the methanol fuel also crosses over from anode towards cathode of the cell. This crossover of the fuel hampers the working of the cell and ultimately its output voltage reduces. This defect of Nafion® paved way for the other membranes to be developed. In this work, the working principle and applications of DMFC will be discussed. Using polyvinyl alcohol (PVA) as the polymer based, the membranes will be incorporated with zeolite dopant that acts as proton carriers. The conducting property of the new composite materials for DMFC showed that the conductivity increase as the temperature increase. The concentration of zeolite in this new membrane ranges between 10% till 50%. Various temperatures ranges between 40°C till 70°C showed the increase of conductivity as the temperature increase. The developed composite membranes are characterized by using SEM for microstructure and impedance analyser for their proton conductivity.




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Fuzzy Classification of Mountains Extracted from Multiscale Digital Elevation Models

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