Abstract: In this paper, half bridge DC-DC converters with
transformer isolation presented in the literature are analyzed for highcurrent
and low-voltage applications under the same operation
conditions, and compared in terms of losses and efficiency. The
conventional and improved half-bridge DC-DC converters are
simulated, and current and voltage waveforms are obtained for input
voltage Vdc=500V, output current IO=450A, output voltage VO=38V
and switching frequency fS=20kHz. IGBTs are used as power
semiconductor switches. The power losses of the semiconductor
devices are calculated from current and voltage waveforms. From
simulation results, it is seen that the capacitor switched half bridge
converter has the best efficiency value, and can be preferred at high
power and high frequency applications.
Abstract: A modified Saleh-Valenzuela channel model has been
adapted for Ultra Wideband (UWB) system. The suggested realistic
channel is assessed by its distribution of fading amplitude and time of
arrivals. Furthermore, the propagation characteristic has been distinct
into four channel models, namely CM 1 to 4. Each are differentiate in
terms of cluster arrival rates, rays arrival rate within each cluster and
its respective constant decay rates. This paper described the
multiband OFDM system performance simulates under these
multipath conditions. Simulation work described in this paper is
based on WiMedia ECMA-368 standard, which has been deployed
for practical implementation of low cost and low power UWB
devices.
Abstract: The 9/11 suicide attacks in New York, Washington, D.C., and Pennsylvania, triggered a number of security responses both in the United States of America and other Countries in the World. Kenya, which is an ally and a close partner to North America and Europe, was not left behind. While many states had been parties to numerous terrorism conventions, their response in implementing them had been slow and needed this catalyst. This special case offered a window of opportunity for many “security conscious" regimes in cementing their legal-criminological and political security apparatus. At the international level, the 9/11 case led to the hasty adoption of Security Council resolution 1373 in 2001, which called upon states to adopt wide-ranging and comprehensive steps and strategies to combat international terrorism and to become parties to the relevant international conventions and protocols relating to terrorism. Since then, Kenya has responded with speed in devising social-legal-criminological-political actions.
Abstract: We depend upon explanation in order to “make sense"
out of our world. And, making sense is all the more important when
dealing with change. But, what happens if our explanations are
wrong? This question is examined with respect to two types of
explanatory model. Models based on labels and categories we shall
refer to as “representations." More complex models involving
stories, multiple algorithms, rules of thumb, questions, ambiguity we
shall refer to as “compressions." Both compressions and
representations are reductions. But representations are far more
reductive than compressions. Representations can be treated as a set
of defined meanings – coherence with regard to a representation is
the degree of fidelity between the item in question and the definition
of the representation, of the label. By contrast, compressions contain
enough degrees of freedom and ambiguity to allow us to make
internal predictions so that we may determine our potential actions in
the possibility space. Compressions are explanatory via mechanism.
Representations are explanatory via category. Managers are often
confusing their evocation of a representation (category inclusion) as
the creation of a context of compression (description of mechanism).
When this type of explanatory error occurs, more errors follow. In
the drive for efficiency such substitutions are all too often proclaimed
– at the manager-s peril..
Abstract: This paper proposes a fast tree join scheme to provide
seamless multicast handover in the mobile networks based on the Fast
Mobile IPv6 (FMIPv6). In the existing FMIPv6-based multicast
handover scheme, the bi-directional tunnelling or the remote
subscription is employed with the packet forwarding from the previous
access router (AR) to the new AR. In general, the remote subscription
approach is preferred to the bi-directional tunnelling one, since in the
remote subscription scheme we can exploit an optimized multicast
path from a multicast source to many mobile receivers. However, in
the remote subscription scheme, if the tree joining operation takes a
long time, the amount of data packets to be forwarded and buffered for
multicast handover will increase, and thus the corresponding buffer
may overflow, which results in severe packet losses. In order to reduce
these costs associated with packet forwarding and buffering, this paper
proposes the fast join to multicast tree, in which the new AR will join
the multicast tree as fast as possible, so that the new multicast data
packets can also arrive at the new AR, by which the packet forwarding
and buffering costs can be reduced. From numerical analysis, it is
shown that the proposed scheme can give better performance than the
existing FMIPv6-based multicast handover schemes in terms of the
multicast packet delivery costs.
Abstract: A model to identify the lifetime of target tracking
wireless sensor network is proposed. The model is a static clusterbased
architecture and aims to provide two factors. First, it is to
increase the lifetime of target tracking wireless sensor network.
Secondly, it is to enable good localization result with low energy
consumption for each sensor in the network. The model consists of
heterogeneous sensors and each sensing member node in a cluster
uses two operation modes–active mode and sleep mode. The
performance results illustrate that the proposed architecture consumes
less energy and increases lifetime than centralized and dynamic
clustering architectures, for target tracking sensor network.
Abstract: Extracting thematic (semantic) roles is one of the
major steps in representing text meaning. It refers to finding the
semantic relations between a predicate and syntactic constituents in a
sentence. In this paper we present a rule-based approach to extract
semantic roles from Persian sentences. The system exploits a twophase
architecture to (1) identify the arguments and (2) label them
for each predicate.
For the first phase we developed a rule based shallow parser to
chunk Persian sentences and for the second phase we developed a
knowledge-based system to assign 16 selected thematic roles to the
chunks. The experimental results of testing each phase are shown at
the end of the paper.
Abstract: Compaction testing methods allow at-speed detecting
of errors while possessing low cost of implementation. Owing to this
distinctive feature, compaction methods have been widely used for
built-in testing, as well as external testing. In the latter case, the
bandwidth requirements to the automated test equipment employed
are relaxed which reduces the overall cost of testing. Concurrent
compaction testing methods use operational signals to detect
misbehavior of the device under test and do not require input test
stimuli. These methods have been employed for digital systems only.
In the present work, we extend the use of compaction methods for
concurrent testing of analog-to-digital converters. We estimate
tolerance bounds for the result of compaction and evaluate the
aliasing rate.
Abstract: In automotive systems almost all steps concerning the
calibration of several control systems, e.g., low idle governor or
boost pressure governor, are made with the vehicle because the timeto-
production and cost requirements on the projects do not allow for
the vehicle analysis necessary to build reliable models. Here is
presented a procedure using parametric and NN (neural network)
models that enables the generation of vehicle system models based
on normal ECU engine control unit) vehicle measurements. These
models are locally valid and permit pre and follow-up calibrations so
that, only the final calibrations have to be done with the vehicle.
Abstract: A big organization may have multiple branches spread across different locations. Processing of data from these branches becomes a huge task when innumerable transactions take place. Also, branches may be reluctant to forward their data for centralized processing but are ready to pass their association rules. Local mining may also generate a large amount of rules. Further, it is not practically possible for all local data sources to be of the same size. A model is proposed for discovering valid rules from different sized data sources where the valid rules are high weighted rules. These rules can be obtained from the high frequency rules generated from each of the data sources. A data source selection procedure is considered in order to efficiently synthesize rules. Support Equalization is another method proposed which focuses on eliminating low frequency rules at the local sites itself thus reducing the rules by a significant amount.
Abstract: As known that efficiency of photovoltaic cells is not
high as desired level. Efficiency of PVs could be improved by
selecting convenient locations that have high solar irradiation,
sunshine duration, mild temperature, low level air pollution and dust
concentration. Additionally, some environmental parameters called
derating factors effect to decrease PV efficiencies such as cloud, high
temperature, aerosol optical depth, high dust concentration, shadow,
snow, humidity etc. In this paper, all parameters that effect PV
efficiency are considered in detail under climatic conditions of
Istanbul. A 750 Wp PV system with measurement devices is
constructed in Maslak campus of Istanbul Technical University.
Abstract: In the present work, an attempt has been made to
understand the feasibility of using UHF technique for identification
of any corona discharges/ arcing in insulating material due to water
droplets. The sensors of broadband type are useful for identification
of such discharges. It is realised that arcing initiated by liquid droplet
radiates UHF signals in the entire bandwidth up to 2 GHz. The
frequency content of the UHF signal generated due to corona/arcing
is not much varied in epoxy nanocomposites with different weight
percentage of clay content. The exfoliated/intercalated properties
were analysed through TEM studies. It is realized that corona
initiated discharges are of intermittent process. The hydrophobicity
of the material characterized through contact angle measurement. It
is realized that low Wt % of nanoclay content in epoxy resin reduces
the surface carbonization due to arcing/corona discharges. The results
of the study with gamma irradiated specimen indicates that contact
angle, discharge inception time and evaporation time of the liquid are
much lower than the virgin epoxy nanocomposite material.
Abstract: A numerical study on the turbulent flow and heat
transfer characteristics in the rectangular channel with different types
of baffles is carried out. The inclined baffles have the width of 19.8
cm, the square diamond type hole having one side length of 2.55 cm,
and the inclination angle of 5o. Reynolds number is varied between
23,000 and 57,000. The SST turbulence model is applied in the
calculation. The validity of the numerical results is examined by the
experimental data. The numerical results of the flow field depict that
the flow patterns around the different baffle type are entirely different
and these significantly affect the local heat transfer characteristics.
The heat transfer and friction factor characteristics are significantly
affected by the perforation density of the baffle plate. It is found that
the heat transfer enhancement of baffle type II (3 hole baffle) has the
best values.
Abstract: Flexible manufacturing system is a system that is able to respond to changed conditions. In general, this flexibility is divided into two key categories and several subcategories. The first category is the so called machine flexibility which enables to make various products by the given machinery. The second category is routing flexibility enabling to execute the same operation by various machines. Flexible manufacturing systems usually consist of three main parts: CNC machine tools, transport system and control system. A higher level of flexible manufacturing systems is represented by the so called intelligent manufacturing systems.
Abstract: This paper presents a conceptual model of agreement
options on negotiation support for civil engineering decision. The
negotiation support facilitates the solving of group choice decision
making problems in civil engineering decision to reduce the impact
of mud volcano disaster in Sidoarjo, Indonesia. The approach based
on application of analytical hierarchy process (AHP) method for
multi criteria decision on three level of decision hierarchy.
Decisions for reducing impact is very complicated since many
parties involved in a critical time. Where a number of stakeholders
are involved in choosing a single alternative from a set of solution
alternatives, there are different concern caused by differing
stakeholder preferences, experiences, and background. Therefore, a
group choice decision support is required to enable each stakeholder
to evaluate and rank the solution alternatives before engaging into
negotiation with the other stakeholders. Such civil engineering
solutions as alternatives are referred to as agreement options that are
determined by identifying the possible stakeholder choice, followed
by determining the optimal solution for each group of stakeholder.
Determination of the optimal solution is based on a game theory
model of n-person general sum game with complete information that
involves forming coalitions among stakeholders.
Abstract: Today, incorrect use of lands and land use changes,
excessive grazing, no suitable using of agricultural farms, plowing on
steep slopes, road construct, building construct, mine excavation etc
have been caused increasing of soil erosion and sediment yield. For
erosion and sediment estimation one can use statistical and empirical
methods. This needs to identify land unit map and the map of
effective factors. However, these empirical methods are usually time
consuming and do not give accurate estimation of erosion. In this
study, we applied GIS techniques to estimate erosion and sediment of
Menderjan watershed at upstream Zayandehrud river in center of
Iran. Erosion faces at each land unit were defined on the basis of land
use, geology and land unit map using GIS. The UTM coordinates of
each erosion type that showed more erosion amounts such as rills and
gullies were inserted in GIS using GPS data. The frequency of
erosion indicators at each land unit, land use and their sediment yield
of these indices were calculated. Also using tendency analysis of
sediment yield changes in watershed outlet (Menderjan hydrometric
gauge station), was calculated related parameters and estimation
errors. The results of this study according to implemented watershed
management projects can be used for more rapid and more accurate
estimation of erosion than traditional methods. These results can also
be used for regional erosion assessment and can be used for remote
sensing image processing.
Abstract: This paper investigates vortex shedding processes
occurring at the end of a stack of parallel plates, due to an oscillating
flow induced by an acoustic standing wave within an acoustic
resonator. Here, Particle Image Velocimetry (PIV) is used to quantify
the vortex shedding processes within an acoustic cycle
phase-by-phase, in particular during the “ejection" of the fluid out of
the stack. Standard hot-wire anemometry measurement is also applied
to detect the velocity fluctuations near the end of the stack.
Combination of these two measurement techniques allowed a detailed
analysis of the vortex shedding phenomena. The results obtained show
that, as the Reynolds number varies (by varying the plate thickness
and drive ratio), different flow patterns of vortex shedding are
observed by the PIV measurement. On the other hand, the
time-dependent hot-wire measurements allow obtaining detailed
frequency spectra of the velocity signal, used for calculating
characteristic Strouhal numbers. The impact of the plate thickness and
the Reynolds number on the vortex shedding pattern has been
discussed. Furthermore, a detailed map of the relationship between the
Strouhal number and Reynolds number has been obtained and
discussed.
Abstract: The iris recognition technology is the most accurate,
fast and less invasive one compared to other biometric techniques
using for example fingerprints, face, retina, hand geometry, voice or
signature patterns. The system developed in this study has the
potential to play a key role in areas of high-risk security and can
enable organizations with means allowing only to the authorized
personnel a fast and secure way to gain access to such areas. The
paper aim is to perform the iris region detection and iris inner and
outer boundaries localization. The system was implemented on
windows platform using Visual C# programming language. It is easy
and efficient tool for image processing to get great performance
accuracy. In particular, the system includes two main parts. The first
is to preprocess the iris images by using Canny edge detection
methods, segments the iris region from the rest of the image and
determine the location of the iris boundaries by applying Hough
transform. The proposed system tested on 756 iris images from 60
eyes of CASIA iris database images.
Abstract: Vortex-shedding phenomenon of the flow
around combined two bodies having various geometries and sizes has been investigated experimentally in the Reynolds
number range between 4.1x103 and 1.75x104. To see the effect
of the rotation of the bodies on the vortex shedding, the
combined bodies were rotated from 0° to 180°. The combined models have a cross section composing of a main circular cylinder and an attached circular or square cylinder. Results
have shown that Strouhal numbers for two cases were
changed considerably with the angle of incidence, while it was found to be largely independent of Reynolds number at 150. Characteristics of the vortex formation region and
location of flow attachments, reattachments, and separations
were observed by means of the flow visualizations.
Depending on the inclination angle the effects of flow
attachment, separation and reattachment on vortex-shedding phenomenon have been discussed.
Abstract: KSLV-I(Korea Space Launch Vehicle-I) is designed as
a launch vehicle to enter a 100 kg-class satellite to the LEO(Low Earth
Orbit). Attitude angles of the upper-stage, including roll, pitch and
yaw are controlled by the cold gas thruster system using nitrogen gas.
The cold gas thruster is an actuator in the RCS(Reaction Control
System). To design an attitude controller for the upper-stage, thrust
measurement in vacuum condition is required. In this paper, the new
thrust measurement system and calibration mechanism are developed
and measurement errors and signal processing method are presented.