Abstract: Pulse width modulation (PWM) techniques have been
the subject of intensive research for different industrial and power
sector applications. A large variety of methods, different in concept
and performance, have been newly developed and described. This
paper analyzes the comparative merits of Sinusoidal Pulse Width
Modulation (SPWM) and Space Vector Pulse Width Modulation
(SVPWM) techniques and the suitability of these techniques in a
Shunt Active Filter (SAF). The objective is to select the scheme that
offers effective utilization of DC bus voltage and also harmonic
reduction at the input side. The effectiveness of the PWM techniques
is tested in the SAF configuration with a non linear load. The
performance of the SAF with the SPWM and (SVPWM) techniques
are compared with respect to the THD in source current. The study
reveals that in the context of closed loop SAF control with the
SVPWM technique there is only a minor improvement in THD. The
utilization of the DC bus with SVPWM is also not significant
compared to that with SPWM because of the non sinusoidal
modulating signal from the controller in SAF configuration.
Abstract: The dramatic effect of information technology on
society is undeniable. In education, it is evident in the use of terms
like active learning, blended learning, electronic learning and mobile
learning (ubiquitous learning). This study explores the perceptions of
54 learners in a higher education institution regarding the use of
mobile devices in a third year module. Using semi-structured
interviews, it was found that mobile devices had a positive impact on
learner motivation, engagement and enjoyment. It also improved the
consistency of learning material, and the convenience and flexibility
(anywhere, anytime) of learning. User-interfacelimitation, bandwidth
and cognitive overload, however, were of concern. The use of cloud
based resources like Youtube and Google Docs, through mobile
devices, positively influenced learner perceptions, making them
prosumers (both consumers and producers) of education content.
Abstract: A rigorous two-dimensional model is developed for simulating the operation of a less-investigated type steam reformer having a considerably lower operating Reynolds number, higher tube diameter, and non-availability of extra steam in the feed compared with conventional steam reformers. Simulation results show that reasonable predictions can only be achieved when certain correlations for wall to fluid heat transfer equations are applied. Due to severe operating conditions, in all cases, strong radial temperature gradients inside the reformer tubes have been found. Furthermore, the results show how a certain catalyst loading profile will affect the operation of the reformer.
Abstract: Since 2005, an SRF module of CESR type serves as the
accelerating cavity at the Taiwan Light Source in the National
Synchrotron Radiation Research Center. A 500-MHz niobium cavity
is immersed in liquid helium inside this SRF module. To reduce heat
load, the liquid helium vessel is thermally shielded by
liquid-nitrogen-cooled copper layer, and the beam chambers are also
anchored with pipes of the liquid nitrogen flow in middle of the liquid
helium vessel and the vacuum vessel. A strong correlation of the
movement of the cavity-s frequency tuner with the temperature
variation of parts cooled with liquid nitrogen was observed. A
previous study on a spare SRF module with the niobium cavity cooled
by liquid nitrogen instead of liquid helium, satisfactory suppression of
the thermal oscillation was achieved by attaching a temporary buffer
tank for the vented shielding nitrogen flow from the SRF module. In
this study, a home-made buffer tank is designed and integrated to the
spare SRF module with cavity cooled by liquid helium. Design,
construction, integration, and preliminary test results of this buffer
tank are presented.
Abstract: Though nonlinear dynamic analysis using a specialized
hydro-code such as AUTODYN is accurate and useful tool for
progressive collapse assessment of a multi-story building subjected to
blast load, it takes too much time to be applied to a practical simulation
of progressive collapse of a tall building. In this paper, blast analysis of
a RC frame structure using a simplified model with Reinforcement
Contact technique provided in Ansys Workbench was introduced and
investigated on its accuracy. Even though the simplified model has a
fraction of elements of the detailed model, the simplified model with
this modeling technique shows similar structural behavior under the
blast load to the detailed model. The proposed modeling method can
be effectively applied to blast loading progressive collapse analysis of
a RC frame structure.
Abstract: A CFD software was employed to analyze the
characteristics of the flat round porous aerostatic bearings. The effects
of gap between the bearing and the guide way and the porosity of the
porous material on the load capacity of the bearing were studied. The
adequacy of the simulation model and the approach was verified. From
the parametric study, it is found that the depth of the flow path does not
influence the load capacity of the bearing; the load capacity of the
bearing will decrease if the thickness of the porous material increases
or the porous material protrudes above the bearing housing; the
variation of the chamfer at the edge of the bearing does not affect the
bearing load capacity. For a bearing with an air gap of 5μm and a
porosity of 0.1, the average load capacity and the pressure distribution
of the bearing are nearly unchanged no matter the bearing moves at a
constant or a varying speed.
Abstract: At any point of time, a power system operating
condition should be stable, meeting various operational criteria and it
should also be secure in the event of any credible contingency. Present
day power systems are being operated closer to their stability limits
due to economic and environmental constraints. Maintaining a stable
and secure operation of a power system is therefore a very important
and challenging issue. Voltage instability has been given much
attention by power system researchers and planners in recent years,
and is being regarded as one of the major sources of power system
insecurity. Voltage instability phenomena are the ones in which the
receiving end voltage decreases well below its normal value and does
not come back even after setting restoring mechanisms such as VAR
compensators, or continues to oscillate for lack of damping against the
disturbances. Reactive power limit of power system is one of the major
causes of voltage instability. This paper investigates the effects of
coordinated series capacitors (SC) with static VAR compensators
(SVC) on steady-state voltage stability of a power system. Also, the
influence of the presence of series capacitor on static VAR
compensator controller parameters and ratings required to stabilize
load voltages at certain values are highlighted.
Abstract: The reluctance motor is an electric motor in which
torque is produced by the tendency of its moveable part to move to a
position where the inductance of the excited winding is maximized.
In this paper switched reluctance motors (SRMs) with two different
configurations(3-phase SRM with 4rotor poles and 6 stator poles, 4-
phase SRM with 6rotor poles and 8 stator poles) is designed by
RMxprt, and performance of them is analyzed. Efficiency and torque
of SRM for different configurations in full-load condition have been
presented. The results indicate that with correct choosing of motor
applications, maximum efficiency can be found.
Abstract: Dealing with hundreds of features in character
recognition systems is not unusual. This large number of features
leads to the increase of computational workload of recognition
process. There have been many methods which try to remove
unnecessary or redundant features and reduce feature dimensionality.
Besides because of the characteristics of Farsi scripts, it-s not
possible to apply other languages algorithms to Farsi directly. In this
paper some methods for feature subset selection using genetic
algorithms are applied on a Farsi optical character recognition (OCR)
system. Experimental results show that application of genetic
algorithms (GA) to feature subset selection in a Farsi OCR results in
lower computational complexity and enhanced recognition rate.
Abstract: This work proposes an accurate crosstalk noise estimation method in the presence of multiple RLC lines for the use in design automation tools. This method correctly models the loading effects of non switching aggressors and aggressor tree branches using resistive shielding effect and realistic exponential input waveforms. Noise peak and width expressions have been derived. The results obtained are at good agreement with SPICE results. Results show that average error for noise peak is 4.7% and for the width is 6.15% while allowing a very fast analysis.
Abstract: This paper presents a method to detect multiple cracks
based on frequency information. When a structure is subjected to
dynamic or static loads, cracks may develop and the modal
frequencies of the cracked structure may change. To detect cracks in a
structure, we construct a high precision wavelet finite element (EF)
model of a certain structure using the B-spline wavelet on the interval
(BSWI). Cracks can be modeled by rotational springs and added to the
FE model. The crack detection database will be obtained by solving
that model. Then the crack locations and depths can be determined
based on the frequency information from the database. The
performance of the proposed method has been numerically verified by
a rotor example.
Abstract: The V-notches are most possible case for initiation of cracks in parts. The specifications of cracks on the tip of the notch will be influenced via opening angle, tip radius and depth of V-notch. In this study, the effects of V-notch-s opening angle on stress intensity factor and T-stress of crack on the notch has been investigated. The experiment has been done in different opening angles and various crack length in mode (I) loading using Photoelasticity method. The results illustrate that while angle increases in constant crack-s length, SIF and T-stress will decrease. Beside, the effect of V-notch angle in short crack is more than long crack. These V-notch affects are negligible by increasing the length of crack, and the crack-s behavior can be considered as a single-edge crack specimen. Finally, the results have been evaluated with numerical finite element analysis and good agreement was obvious.
Abstract: In the competitive environment of aircraft industries it becomes absolutely necessary to improve the efficiency, performance of the aircrafts to reduce the development and operating costs considerably, in order to capitalize the market. An important contribution to improve the efficiency and performance can be
achieved by decreasing the aircraft weight through considerable
usage of composite materials in primary aircraft structures. In this study, a type of composite material called Carbon Fiber Reinforced
Plastic (CFRP) is explored for the usage is aircraft skin panels. Even
though there were plenty of studies and research has been already
carried out, here a practical example of an aircraft skin panel is taken
and substantiated the benefits of composites material usage over the
metallic skin panel. A crown skin panel of a commercial aircraft is
designed using both metal and composite materials. Stress analysis
has been carried out for both and margin of safety is estimated for the
critical load cases. The skin panels are compared for manufacturing,
tooling, assembly and cost parameters. Detail step by step comparison between metal and composite constructions are studied
and results are tabulated for better understanding.
Abstract: To date, theoretical studies concerning the Carbon
Fiber Reinforced Polymer (CFRP) strengthening of RC beams with
openings have been rather limited. In addition, various numerical
analyses presented so far have effectively simulated the behaviour of
solid beam strengthened by FRP material. In this paper, a two
dimensional nonlinear finite element analysis is presented to validate
against the laboratory test results of six RC beams. All beams had the
same rectangular cross-section geometry and were loaded under four
point bending. The crack pattern results of the finite element model
show good agreement with the crack pattern of the experimental
beams. The load midspan deflection curves of the finite element
models exhibited a stiffer result compared to the experimental beams.
The possible reason may be due to the perfect bond assumption used
between the concrete and steel reinforcement.
Abstract: The speculative locking (SL) protocol extends the twophase locking (2PL) protocol to allow for parallelism among conflicting transactions. The adaptive speculative locking (ASL) protocol provided further enhancements and outperformed SL protocols under most conditions. Neither of these protocols consider the impact of network latency on the performance of the distributed database systems. We have studied the performance of ASL protocol taking into account the communication overhead. The results indicate that though system load can counter network latency, it can still become a bottleneck in many situations. The impact of latency on performance depends on many factors including the system resources. A flexible discrete event simulator was used as the testbed for this study.
Abstract: The aims of this paper are to study the efficacy of
chitosan nanoparticles in stimulating specific antibody against
A/H1N1 influenza antigen in mice. Chitosan nanoparticles (CSN)
were characterized by TEM. The results showed that the average size
of CSN was from 80nm to 106nm. The efficacy of A/H1N1 influenza
vaccine loaded on the surface of CSN showed that loading efficiency
of A/H1N1 influenza antigen on CSN was from 93.75 to 100%. Safe
property of the vaccine were tested. In 10 days post vaccination,
group of CSN 30 kDa and 300 kDa loaded A/H1N1 influenza antigen
were the rate of immune response on mice to be 100% (9/9) higher
than Al(OH)3 and other adjuvant. 100% mice in the experiment of all
groups had immune response in 20 days post vaccination. The results
also showed that HI titer of the group using CSN 300 kDa as an
adjuvant increased significantly up to 3971 HIU, over three-fold
higher than the Al(OH)3 adjuvant, chitosan (CS), and one hundredfold
than the A/H1N1 antigen only. Stability of the vaccine
formulation was investigated.
Abstract: The mechanical properties including flexural and
tensile of neat vinyl ester and polymer based on layered silicate
nanocomposite materials are discussed. The addition of layered
silicate into the polymer matrix increased the tensile and flexural
modulus up to 1 wt.% clay loading. The incorporation of more clay
resulted in decreasing the mechanical properties which was traced to
the existence of aggregation layers. Likewise, up to 1 wt.% clay
loading, the thermal behaviour showed significant improvements and
at higher clay loading the thermal pattern was reduced. The
aggregation layers imparted a negative impact on the overall
mechanical and thermal properties. Wide Angle X-ray Diffraction,
Scanning Electron Microscopy and Transmission Electron
Microscopy were utilised in order to characterise the interlamellar
structure of nanocomposites.
Abstract: The analytical solution of functionally graded
piezoelectric hollow cylinder which is under radial electric potential
and non-axisymmetric thermo-mechanical loads, are presented in this
paper. Using complex Fourier series and estimation of power law for
variations of material characterizations through the thickness, the
electro thermo mechanical behavior of the FGPM cylinder is
obtained. The stress and displacement distributions and the effect of
electric potential field on the cylinder behavior are also presented and
some applicable results are offered at the end of the paper.
Abstract: The presence of harmonic in power system is a major
concerned to power engineers for many years. With the increasing
usage of nonlinear loads in power systems, the harmonic pollution
becomes more serious. One of the widely used computation
algorithm for harmonic analysis is fast Fourier transform (FFT). In
this paper, a harmonic analyzer using FFT was implemented on
TMS320C6713 DSK. The supply voltage of 240 V 59 Hz is stepped
down to 5V using a voltage divider in order to match the power
rating of the DSK input. The output from the DSK was displayed on
oscilloscope and Code Composer Studio™ software. This work has
demonstrated the possibility of analyzing the 240V power supply
harmonic content using the DSK board.
Abstract: Air emissions from waste treatment plants often
consist of a combination of Volatile Organic Compounds (VOCs)
and odors. Hydrogen sulfide is one of the major odorous gases
present in the waste emissions coming from municipal wastewater
treatment facilities. Hydrogen sulfide (H2S) is odorous, highly toxic
and flammable. Exposure to lower concentrations can result in eye
irritation, a sore throat and cough, shortness of breath, and fluid in
the lungs. Biofiltration has become a widely accepted technology for
treating air streams containing H2S. When compared with other nonbiological
technologies, biofilter is more cost-effective for treating large
volumes of air containing low concentrations of biodegradable compounds.
Optimization of biofilter media is essential for many reasons such as:
providing a higher surface area for biofilm growth, low pressure drop,
physical stability, and good moisture retention. In this work, a novel
biofilter media is developed and tested at a pumping station of a
municipality located in the United Arab Emirates (UAE). The
media is found to be very effective (>99%) in removing H2S
concentrations that are expected in pumping stations under steady
state and shock loading conditions.