Abstract: Nowadays in applications of renewable energy sources
it is important to develop powerful and energy-saving photovoltaic
converters and to keep the prescriptions of the standards. In grid
connected PV converters the obvious solution to increase the
efficiency is to reduce the switching losses. Our new developed
control method reduces the switching losses and keeps the limitations
of the harmonic distortion standards. The base idea of the method is
the utilization of 3-state control causing discontinuous current mode
at low input power. In the following sections the control theory, the
realizations and the simulation results are presented.
Abstract: Restoration of endodontically treated teeth is a
common problem in dentistry, related to the fractures occurring in
such teeth and to concentration of forces little information regarding
variation of basic preparation guidelines in stress distribution has
been available. To date, there is still no agreement in the literature
about which material or technique can optimally restore
endodontically treated teeth. The aim of the present study was to
evaluate the influence of the core height and restoration materials on
corono-radicular restored upper first premolar. The first step of the
study was to achieve 3D models in order to analyze teeth, dowel and
core restorations and overlying full ceramic crowns. The FEM model
was obtained by importing the solid model into ANSYS finite
element analysis software. An occlusal load of 100 N was conducted,
and stresses occurring in the restorations, and teeth structures were
calculated. Numerical simulations provide a biomechanical
explanation for stress distribution in prosthetic restored teeth. Within
the limitations of the present study, it was found that the core height
has no important influence on the stress generated in coronoradicular
restored premolars. It can be drawn that the cervical regions
of the teeth and restorations were subjected to the highest stress
concentrations.
Abstract: Global approximation using metamodel for complex
mathematical function or computer model over a large variable
domain is often needed in sensibility analysis, computer simulation,
optimal control, and global design optimization of complex, multiphysics
systems. To overcome the limitations of the existing
response surface (RS), surrogate or metamodel modeling methods for
complex models over large variable domain, a new adaptive and
regressive RS modeling method using quadratic functions and local
area model improvement schemes is introduced. The method applies
an iterative and Latin hypercube sampling based RS update process,
divides the entire domain of design variables into multiple cells,
identifies rougher cells with large modeling error, and further divides
these cells along the roughest dimension direction. A small number
of additional sampling points from the original, expensive model are
added over the small and isolated rough cells to improve the RS
model locally until the model accuracy criteria are satisfied. The
method then combines local RS cells to regenerate the global RS
model with satisfactory accuracy. An effective RS cells sorting
algorithm is also introduced to improve the efficiency of model
evaluation. Benchmark tests are presented and use of the new
metamodeling method to replace complex hybrid electrical vehicle
powertrain performance model in vehicle design optimization and
optimal control are discussed.
Abstract: Laser interferometric methods have been utilized for the measurement of natural convection heat transfer from a heated vertical flat plate, in the investigation presented here. The study mainly aims at comparing two different fringe orientations in the wedge fringe setting of Mach-Zehnder interferometer (MZI), used for the measurements. The interference fringes are set in horizontal and vertical orientations with respect to the heated surface, and two different fringe analysis methods, namely the stepping method and the method proposed by Naylor and Duarte, are used to obtain the heat transfer coefficients. The experimental system is benchmarked with theoretical results, thus validating its reliability in heat transfer measurements. The interference fringe patterns are analyzed digitally using MATLAB 7 and MOTIC Plus softwares, which ensure improved efficiency in fringe analysis, hence reducing the errors associated with conventional fringe tracing. The work also discuss the relative merits and limitations of the two methods used.
Abstract: Antimicrobial (AM) starch-based films were
developed by incorporating chitosan and lauric acid as antimicrobial
agent into starch-based film. Chitosan has wide range of applications
as a biomaterial, but barriers still exist to its broader use due to its
physical and chemical limitations. In this work, a series of
starch/chitosan (SC) blend films containing 8% of lauric acid was
prepared by casting method. The structure of the film was
characterized by Fourier transform infrared spectroscopy (FTIR), Xray
diffraction (XRD), and scanning electron microscopy (SEM).
The results indicated that there were strong interactions were present
between the hydroxyl groups of starch and the amino groups of
chitosan resulting in a good miscibility between starch and chitosan
in the blend films. Physical properties and optical properties of the
AM starch-based film were evaluated. The AM starch-based films
incorporated with chitosan and lauric acid showed an improvement in
water vapour transmission rate (WVTR) and addition of starch
content provided more transparent films while the yellowness of the
film attributed to the higher chitosan content. The improvement in
water barrier properties was mainly attributed to the hydrophobicity
of lauric acid and optimum chitosan or starch content. AM starch
based film also showed excellent oxygen barrier. Obtaining films
with good oxygen permeability would be an indication of the
potential use of these antimicrobial packaging as a natural packaging
and an alternative packaging to the synthetic polymer to protect food
from oxidation reactions
Abstract: This research aimed at investigating the Cr (III), Cd
(II) and Pb (II) removal efficiencies by using the newly synthesized
metal oxides/ polyethersulfone (PES), Al2O3/PES and ZrO2/PES,
membranes from synthetic wastewater and exploring fouling
mechanisms. A Comparative study between the removal efficiencies
of Cr (III), Cd (II) and Pb (II) from synthetic and natural wastewater
by using adsorption onto agricultural by products and the newly
synthesized Al2O3/PES and ZrO2/PES membranes was conducted to
assess the advantages and limitations of using the metal oxides/PES
membranes for heavy metals removal. The results showed that about
99 % and 88 % removal efficiencies were achieved by the tested
membranes for Pb (II) and Cr (III), respectively.
Abstract: The Address Resolution Protocol (ARP) is used by
computers to map logical addresses (IP) to physical addresses
(MAC). However ARP is an all trusting protocol and is stateless
which makes it vulnerable to many ARP cache poisoning attacks
such as Man-in-the-Middle (MITM) and Denial of service (DoS)
attacks. These flaws result in security breaches thus weakening the
appeal of the computer for exchange of sensitive data. In this paper
we describe ARP, outline several possible ARP cache poisoning
attacks and give the detailed of some attack scenarios in network
having both wired and wireless hosts. We have analyzed each of
proposed solutions, identify their strengths and limitations. Finally
get that no solution offers a feasible solution. Hence, this paper
presents an efficient and secure version of ARP that is able to cope
up with all these types of attacks and is also a feasible solution. It is a
stateful protocol, by storing the information of the Request frame in
the ARP cache, to reduce the chances of various types of attacks in
ARP. It is more efficient and secure by broadcasting ARP Reply
frame in the network and storing related entries in the ARP cache
each time when communication take place.
Abstract: Nowadays the construction industry is growing specially among developing counties. Iran also has a critical role in these industries in terms of workers disorders. Work-related musculoskeletal disorders (WMSDs) assign 7% of the whole diseases in the society, which make some limitations. One of the main factors, which are ended to WMSDs, is awkward posture. Steel bar bending is considered as one of the prominent performance among construction workers. In this case study we conducted to find the major tasks of bar benders and the most important related risk factors. This study was carried out among twenty workers (18-45 years) as our volunteer samples in some construction sites with less than 6 floors in two regions of Tehran municipality. The data was gathered through in depth observation, interview and questionnaire. Also postural analysis was done by OWAS. In another part of study we used NMQ for gathering some data about psychosocial effects of work related disorders. Our findings show that 64% of workers were not aware of work risks, also about 59% of workers had troubles in their wrists, hands, and especially among workers who worked in steel bar bending. In 46% cases low back pain were prevalence. Considering with gathered data and results, awkward postures and long term tasks and its duration are known as the main risk factors in WMSDs among construction workers, so work-rest schedule and also tools design should be considered to make an ergonomic condition for the mentioned workers.
Abstract: The demand for autonomous resource
management for distributed systems has increased in recent
years. Distributed systems require an efficient and powerful
communication mechanism between applications running on
different hosts and networks. The use of mobile agent
technology to distribute and delegate management tasks
promises to overcome the scalability and flexibility limitations
of the currently used centralized management approach. This
work proposes a multiagent system that adopts mobile agents
as a technology for tasks distribution, results collection, and
management of resources in large-scale distributed systems. A
new mobile agent-based approach for collecting results from
distributed system elements is presented. The technique of
artificial intelligence based on intelligent agents giving the
system a proactive behavior. The presented results are based
on a design example of an application operating in a mobile
environment.
Abstract: During the last few years, several sheet hydroforming
processes have been introduced. Despite the advantages of these
methods, they have some limitations. Of the processes, the two main
ones are the standard hydroforming and hydromechanical deep
drawing. A new sheet hydroforming die set was proposed that has the
advantages of both processes and eliminates their limitations. In this
method, a polyurethane plate was used as a part of the die-set to
control the blank holder force. This paper outlines the Taguchi
optimization methodology, which is applied to optimize the effective
parameters in forming cylindrical cups by the new die set of sheet
hydroforming process. The process parameters evaluated in this
research are polyurethane hardness, polyurethane thickness, forming
pressure path and polyurethane hole diameter. The design of
experiments based upon L9 orthogonal arrays by Taguchi was used
and analysis of variance (ANOVA) was employed to analyze the
effect of these parameters on the forming pressure. The analysis of
the results showed that the optimal combination for low forming
pressure is harder polyurethane, bigger diameter of polyurethane hole
and thinner polyurethane. Finally, the confirmation test was derived
based on the optimal combination of parameters and it was shown
that the Taguchi method is suitable to examine the optimization
process.
Abstract: There are various solutions for improving existing overhead line systems with the general purpose of increasing their limited capacity. The capacity reserve of the existing overhead lines is an important problem that must be considered from different aspects. The paper contains a comparative analysis of the mechanical and thermal limitations of an existing overhead line based on certain calculation conditions characterizing the examined variants. The methodology of the proposed estimation of the permissible conductor temperature and maximum load current is described in detail. The transmission line model consists of specific information of an existing overhead line of the Latvian power network. The main purpose of the simulation tasks is to find an additional capacity reserve by using accurate mathematical models. The results of the obtained data are presented.
Abstract: Locality Sensitive Hashing (LSH) is one of the most
promising techniques for solving nearest neighbour search problem in
high dimensional space. Euclidean LSH is the most popular variation
of LSH that has been successfully applied in many multimedia
applications. However, the Euclidean LSH presents limitations that
affect structure and query performances. The main limitation of the
Euclidean LSH is the large memory consumption. In order to achieve
a good accuracy, a large number of hash tables is required. In this
paper, we propose a new hashing algorithm to overcome the storage
space problem and improve query time, while keeping a good
accuracy as similar to that achieved by the original Euclidean LSH.
The Experimental results on a real large-scale dataset show that the
proposed approach achieves good performances and consumes less
memory than the Euclidean LSH.
Abstract: This article investigated the validity of C-test and Cloze test which purport to measure general English proficiency. To provide empirical evidence pertaining to the validity of the interpretations based on the results of these integrative language tests, their criterion-related validity was investigated. In doing so, the test of English as a foreign language (TOEFL) which is an established, standardized, and internationally administered test of general English proficiency was used as the criterion measure. Some 90 Iranian English majors participated in this study. They were seniors studying English at a university in Tehran, Iran. The results of analyses showed that there is a statistically significant correlation among participants- scores on Cloze test, C-test, and the TOEFL. Building on the findings of the study and considering criterion-related validity as the evidential basis of the validity argument, it was cautiously deducted that these tests measure the same underlying trait. However, considering the limitations of using criterion measures to validate tests, no absolute claims can be made as to the construct validity of these integrative tests.
Abstract: Caching was suggested as a solution for reducing bandwidth utilization and minimizing query latency in mobile environments. Over the years, different caching approaches have been proposed, some relying on the server to broadcast reports periodically informing of the updated data while others allowed the clients to request for the data whenever needed. Until recently a hybrid cache consistency scheme Scalable Asynchronous Cache Consistency Scheme SACCS was proposed, which combined the two different approaches benefits- and is proved to be more efficient and scalable. Nevertheless, caching has its limitations too, due to the limited cache size and the limited bandwidth, which makes the implementation of cache replacement strategy an important aspect for improving the cache consistency algorithms. In this thesis, we proposed a new cache replacement strategy, the Least Unified Value strategy (LUV) to replace the Least Recently Used (LRU) that SACCS was based on. This paper studies the advantages and the drawbacks of the new proposed strategy, comparing it with different categories of cache replacement strategies.
Abstract: Offset Double-Disk Opener (DDO) is a popular
furrow opener in conservation tillage. It has some limitations such as
negative suction to penetrate in the soil, hair pinning and mixing seed
and fertilizer in the slot. Because of importance of separation of seed
and fertilizer in the slot, by adding two horizontal mini disks to DDO
a modified opener was made (MDO) which placed the fertilizer
between and under two rows of seed. To consider performance of
novel opener an indoor comparison test between DDO and MDO was
performed at soil bin. The experiment was conducted with three
working speeds (3, 6 and 8 km h-1), two bulk densities of soil (1.1
and 1.4 Mg m-3) and two levels of residues (1 and 2 ton ha-1). The
experimental design consisted in a (3×2×2) complete randomized
factorial with three replicates for each test. Moisture of seed furrow,
separation of seed and fertilizer, hair pinning and resultant forces
acting on the openers were used as assessing indexes. There was no
significant difference between soil moisture content in slots created
by DDO and MDO at 0-4 cm depth, but at 4-8 cm the in the slot
created by MDO moisture content was higher about 9%. Horizontal
force for both openers increased with increasing speed and soil bulk
density. Vertical force for DDO was negative so it needed additional
weight for penetrating in the soil, but vertical force for MDO was
positive and, which can solve the challenge of penetration in the soil
in DDO. In soft soil with heavy residues some trash was pushed by
DDO into seed furrow (hair pinning) but at MDO seed were placed at
clean groove. Lateral and vertical separation of seed and fertilizer
was performed effectively by MDO (4.5 and 5 cm, respectively)
while DDO put seed and fertilizer close to each other. Overall, the
Modified Offset Double-disks (MDO) had better performance. So by
adapting this opener with no-tillage drillers it would possible to have
higher yield in conservation tillage where the most appropriate
opener is disk type.
Abstract: The proper design of RF pulses in magnetic resonance imaging (MRI) has a direct impact on the quality of acquired images, and is needed for many applications. Several techniques have been proposed to obtain the RF pulse envelope given the desired slice profile. Unfortunately, these techniques do not take into account the limitations of practical implementation such as limited amplitude resolution. Moreover, implementing constraints for special RF pulses on most techniques is not possible. In this work, we propose to develop an approach for designing optimal RF pulses under theoretically any constraints. The new technique will pose the RF pulse design problem as a combinatorial optimization problem and uses efficient techniques from this area such as genetic algorithms (GA) to solve this problem. In particular, an objective function will be proposed as the norm of the difference between the desired profile and the one obtained from solving the Bloch equations for the current RF pulse design values. The proposed approach will be verified using analytical solution based RF simulations and compared to previous methods such as Shinnar-Le Roux (SLR) method, and analysis, selected, and tested the options and parameters that control the Genetic Algorithm (GA) can significantly affect its performance to get the best improved results and compared to previous works in this field. The results show a significant improvement over conventional design techniques, select the best options and parameters for GA to get most improvement over the previous works, and suggest the practicality of using of the new technique for most important applications as slice selection for large flip angles, in the area of unconventional spatial encoding, and another clinical use.
Abstract: In this paper, a novel corner detection method is
presented to stably extract geometrically important corners.
Intensity-based corner detectors such as the Harris corner can detect
corners in noisy environments but has inaccurate corner position and
misses the corners of obtuse angles. Edge-based corner detectors such
as Curvature Scale Space can detect structural corners but show
unstable corner detection due to incomplete edge detection in noisy
environments. The proposed image-based direct curvature estimation
can overcome limitations in both inaccurate structural corner detection
of the Harris corner detector (intensity-based) and the unstable corner
detection of Curvature Scale Space caused by incomplete edge
detection. Various experimental results validate the robustness of the
proposed method.
Abstract: Transpedicular screw fixation in spinal fractures,
degenerative changes, or deformities is a well-established procedure.
However, important rate of fixation failure due to screw bending,
loosening, or pullout are still reported particularly in weak bone stock
in osteoporosis. To overcome the problem, mechanism of failure has
to be fully investigated in vitro. Post-mortem human subjects are less
accessible and animal cadavers comprise limitations due to different
geometry and mechanical properties. Therefore, the development of a
synthetic model mimicking the realistic human vertebra is highly
demanded. A bone surrogate, composed of Polyurethane (PU) foam
analogous to cancellous bone porous structure, was tested for 3
different densities in this study. The mechanical properties were
investigated under uniaxial compression test by minimizing the end
artifacts on specimens. The results indicated that PU foam of 0.32
g.cm-3 density has comparable mechanical properties to human
cancellous bone in terms of young-s modulus and yield strength.
Therefore, the obtained information can be considered as primary
step for developing a realistic cancellous bone of human vertebral
body. Further evaluations are also recommended for other density
groups.
Abstract: This research elaborates decision models for product
innovation in the early phases, focusing on one of the most widely
implemented method in marketing research: conjoint analysis and the
related conjoint-based models with special focus on heuristics
programming techniques for the development of optimal product
innovation. The concept, potential, requirements and limitations of
conjoint analysis and its conjoint-based heuristics successors are
analysed and the development of conceptual framework of Genetic
Algorithm (GA) as one of the most widely implemented heuristic
methods for developing product innovations are discussed.
Abstract: In Data mining, Fuzzy clustering algorithms have
demonstrated advantage over crisp clustering algorithms in dealing
with the challenges posed by large collections of vague and uncertain
natural data. This paper reviews concept of fuzzy logic and fuzzy
clustering. The classical fuzzy c-means algorithm is presented and its
limitations are highlighted. Based on the study of the fuzzy c-means
algorithm and its extensions, we propose a modification to the cmeans
algorithm to overcome the limitations of it in calculating the
new cluster centers and in finding the membership values with
natural data. The efficiency of the new modified method is
demonstrated on real data collected for Bhutan-s Gross National
Happiness (GNH) program.