Abstract: Sound attenuation in absorptive silencers has been analyzed in this paper. The structure of such devices is as follows. When the rigid duct of an expansion chamber has been lined by a packed absorptive material under a perforated membrane, incident sound waves will be dissipated by the absorptive liners. This kind of silencer, usually are applicable for medium to high frequency ranges. Several conditions for different absorptive materials, variety in their thicknesses, and different shapes of the expansion chambers have been studied in this paper. Also, graphs of sound attenuation have been compared between empty expansion chamber and duct of silencer with applying liner. Plane waves have been assumed in inlet and outlet regions of the silencer. Presented results that have been achieved by applying finite element method (FEM), have shown the dependence of the sound attenuation spectrum to flow resistivity and the thicknesses of the absorptive materials, and geometries of the cross section (configuration of the silencer). As flow resistivity and thickness of absorptive materials increase, sound attenuation improves. In this paper, diagrams of the transmission loss (TL) for absorptive silencers in five different cross sections (rectangle, circle, ellipse, square, and rounded rectangle as the main geometry) have been presented. Also, TL graphs for silencers using different absorptive material (glass wool, wood fiber, and kind of spongy materials) as liner with three different thicknesses of 5 mm, 15 mm, and 30 mm for glass wool liner have been exhibited. At first, the effect of substances of the absorptive materials with the specific flow resistivity and densities on the TL spectrum, then the effect of the thicknesses of the glass wool, and at last the efficacy of the shape of the cross section of the silencer have been investigated.
Abstract: Regional variations in strong ground motions for the Iranian Plateau have been investigated by using a simple statistical method called Analysis of Variance (ANOVA). In this respect, a large database consisting of 1157 records occurring within the Iranian Plateau with moment magnitudes of greater than or equal to 5 and Joyner-Boore distances up to 200 km has been considered. Geometric averages of horizontal peak ground accelerations (PGA) as well as 5% damped linear elastic response spectral accelerations (SA) at periods of 0.2, 0.5, 1.0, and 2.0 sec are used as strong motion parameters. The initial database is divided into two different datasets, for Northern Iran (NI) and Central and Southern Iran (CSI). The comparison between strong ground motions of these two regions reveals that there is no evidence for significant differences; therefore, data from these two regions may be combined to estimate the unknown coefficients of attenuation relationships.
Abstract: A torsional piezoelectric ultrasonic transducer design
is proposed to measure shear moduli in soft tissue with direct
access availability, using shear wave elastography technique. The
measurement of shear moduli of tissues is a challenging problem,
mainly derived from a) the difficulty of isolating a pure shear wave,
given the interference of multiple waves of different types (P, S,
even guided) emitted by the transducers and reflected in geometric
boundaries, and b) the highly attenuating nature of soft tissular
materials. An immediate application, overcoming these drawbacks,
is the measurement of changes in cervix stiffness to estimate the
gestational age at delivery. The design has been optimized using
a finite element model (FEM) and a semi-analytical estimator of
the probability of detection (POD) to determine a suitable geometry,
materials and generated waves. The technique is based on the time
of flight measurement between emitter and receiver, to infer shear
wave velocity. Current research is centered in prototype testing and
validation. The geometric optimization of the transducer was able
to annihilate the compressional wave emission, generating a quite
pure shear torsional wave. Currently, mechanical and electromagnetic
coupling between emitter and receiver signals are being the research
focus. Conclusions: the design overcomes the main described
problems. The almost pure shear torsional wave along with the short
time of flight avoids the possibility of multiple wave interference.
This short propagation distance reduce the effect of attenuation, and
allow the emission of very low energies assuring a good biological
security for human use.
Abstract: Green roof system is considered a relatively new
concept in Malaysia even though it has been implemented widely in
the developed countries. Generally, green roofs provide many
benefits such as enhancing aesthetical quality of the built
environment, reduce urban heat island effect, reduce energy
consumption, improve stormwater attenuation, and reduce noise
pollution. A better understanding on the implementation of green roof
system in Malaysia is crucial, as Malaysia’s climate is different if
compared with the climate in temperate countries where most of the
green roof studies have been conducted. This study has concentrated
on the technical aspect of green roof system which focuses on i) types
of plants and method of planting; ii) engineering design for green
roof system; iii) its hydrological performance on reducing stormwater
runoff; and iv) benefits of green roofs with respect to energy.
Literature review has been conducted to identify the development and
obstacles associated with green roofs systems in Malaysia. The study
had identified the challenges and potentials of green roofs
development in Malaysia. This study also provided the
recommendations on standard design and strategies on the
implementation of green roofs in Malaysia in the near future.
Abstract: Geological structure formed by volcanic activities shows polymorphic characteristics due to repeated cooling and hardening of lava. The Jeju region is showing polymorphic characteristics in which clinker layers are irregularly distributed along with vesicular basalt due to volcanic activities. Accordingly, resident damages and environmental disputes occur frequently in the Jeju region due to blasting. The purpose of this study is to develop a blast vibration equation considering the polymorphic characteristics of basaltic ground in Jeju. The blast vibration equation consists of a functional formula of the blasting vibration constant K that changes according to ground characteristics, and attenuation index n. The case study results in Jeju showed that if there are clinker layers, attenuation index n showed a distribution of -1.32~-1.81, whereas if there are no clinker layers, n was -2.79. Moreover, if there are no clinker layers, the frequency of blast vibration showed a high frequency band from 30Hz to 100Hz, while in rocks with clinker layers it showed a low frequency band from 10Hz to 20Hz.
Abstract: The occurrences of precipitation, also commonly
referred as rain, in the form of "convective" and "stratiform" have
been identified to exist worldwide. In this study, the radar return
echoes or known as reflectivity values acquired from radar scans
have been exploited in the process of classifying the type of rain
endured. The investigation use radar data from Malaysian
Meteorology Department (MMD). It is possible to discriminate the
types of rain experienced in tropical region by observing the vertical
characteristics of the rain structure. .Heavy rain in tropical region
profoundly affects radiowave signals, causing transmission
interference and signal fading. Required wireless system fade margin
depends on the type of rain. Information relating to the two
mentioned types of rain is critical for the system engineers and
researchers in their endeavour to improve the reliability of
communication links. This paper highlights the quantification of
percentage occurrences over one year period in 2009.
Abstract: Geological and tectonic framework indicates that
Bangladesh is one of the most seismically active regions in the world.
The Bengal Basin is at the junction of three major interacting plates:
the Indian, Eurasian, and Burma Plates. Besides there are many
active faults within the region, e.g. the large Dauki fault in the north.
The country has experienced a number of destructive earthquakes due
to the movement of these active faults. Current seismic provisions of
Bangladesh are mostly based on earthquake data prior to the 1990.
Given the record of earthquakes post 1990, there is a need to revisit
the design provisions of the code. This paper compares the base shear
demand of three major cities in Bangladesh: Dhaka (the capital city),
Sylhet, and Chittagong for earthquake scenarios of magnitudes
7.0MW, 7.5MW, 8.0MW, and 8.5MW using a stochastic model. In
particular, the stochastic model allows the flexibility to input region
specific parameters such as shear wave velocity profile (that were
developed from Global Crustal Model CRUST2.0) and include the
effects of attenuation as individual components. Effects of soil
amplification were analysed using the Extended Component
Attenuation Model (ECAM). Results show that the estimated base
shear demand is higher in comparison with code provisions leading to
the suggestion of additional seismic design consideration in the study
regions.
Abstract: In the cooperative transmission scheme, both the
cellular system and broadcasting system are composed. Two cellular
base stations (CBSs) communicating with a user in the cell edge use
cooperative transmission scheme in the conventional scheme. In the
case that the distance between two CBSs and the user is distant, the
conventional scheme does not guarantee the quality of the
communication because the channel condition is bad. Therefore, if the
distance between CBSs and a user is distant, the performance of the
conventional scheme is decreased. Also, the bad channel condition has
bad effects on the performance. The proposed scheme uses two relays
to communicate well with CBSs when the channel condition between
CBSs and the user is poor. Using the relay in the high attenuation
environment can obtain both advantages of the high bit error rate
(BER) and throughput performance.
Abstract: Acoustic properties of polymeric liquids are high
sensitive to free gas traces in the form of fine bubbles. Their presence
is typical for such liquids because of chemical reactions, small
wettability of solid boundaries, trapping of air in technological
operations, etc. Liquid temperature influences essentially its
rheological properties, which may have an impact on the bubble
pulsations and sound propagation in the system. The target of the
paper is modeling of the liquid temperature effect on single bubble
dynamics and sound dispersion and attenuation in polymeric solution
with spherical gas bubbles. The basic sources of attenuation (heat
exchange between gas in microbubbles and surrounding liquid,
rheological and acoustic losses) are taken into account. It is supposed
that in the studied temperature range the interface mass transfer has a
minor effect on bubble dynamics. The results of the study indicate
that temperature raise yields enhancement of bubble pulsations and
increase in sound attenuation in the near-resonance range and may
have a strong impact on sound dispersion in the liquid-bubble
mixture at frequencies close to the resonance frequency of bubbles.
Abstract: Ibeno, Nigeria hosts the operational base of Mobil
Producing Nigeria Unlimited (MPNU), a subsidiary of ExxonMobil
and the current highest oil & condensate producer in Nigeria. Besides
MPNU, other oil companies operate onshore, on the continental shelf
and deep offshore of the Atlantic Ocean in Ibeno, Nigeria. This study
was designed to delineate oil polluted sites in Ibeno, Nigeria using
geophysical methods of electrical resistivity (ER) and ground
penetrating radar (GPR). Results obtained revealed that there have
been hydrocarbon contaminations of this environment by past crude
oil spills as observed from high resistivity values and GPR profiles
which clearly show the distribution, thickness and lateral extent of
hydrocarbon contamination as represented on the radargram reflector
tones. Contaminations were of varying degrees, ranging from slight
to high, indicating levels of substantial attenuation of crude oil
contamination over time. Moreover, the display of relatively lower
resistivities of locations outside the impacted areas compared to
resistivity values within the impacted areas and the 3-D Cartesian
images of oil contaminant plume depicted by red, light brown and
magenta for high, low and very low oil impacted areas, respectively
confirmed significant recent pollution of the study area with crude
oil.
Abstract: Azadirachta excelsa or locally known as sentang are
frequently used as a traditional medicine by diabetes patients in
Malaysia. However, less attention has been given to their toxicity
effect. Thus, the study is an attempt to examine the protective effect
of A. excelsa on the pancreas and to determine possible toxicity
mediated by the extract. Diabetes was induced experimentally in rats
by high-fat-diet for 16 weeks followed by intraperitoneal injection of
streptozotocin at dosage of 35 mg/kg of body weight. Declination of
the fasting blood glucose level was observed after continuous
administration of A. excelsa for 14 days twice daily. This is due to the
refining structure of the pancreas. However, surprisingly, the plant
extract reduced the leukocytes, erythrocytes, hemoglobin, MCHC and
lymphocytes. In addition, the rat treated with the plant extract
exhibited increment in AST and eosinocytes level. Overall, the
finding shows that A. excelsa possesses antidiabetic activity by
improving the structure of pancreatic islet of Langerhans but
involved in ameliorating of hematology and biochemical parameters.
Abstract: A methodology is proposed for estimating the optical
attenuation and proportional depth variation of shallow inland water.
The process is demonstrated with EO-1 Hyperion hyperspectral and
IRS-P6 LISS-3 multispectral images of Kolkata city nearby area
centered around 22º33′ N 88º26′ E. The attenuation coefficient of
water was found to change with fine resolution of wavebands and in
presence of suspended organic matter in water.
Abstract: Fluid rheology may have essential impact on sound propagation in a liquid-filled pipe, especially, in a low frequency range. Rheological parameters of liquid are temperature-sensitive, which ultimately results in a temperature dependence of the wave speed and attenuation in the waveguide. The study is devoted to modeling of this effect at sound propagation in an elastic pipe with polymeric liquid, described by generalized Maxwell model with non-zero high-frequency viscosity. It is assumed that relaxation spectrum is distributed according to the Spriggs law; temperature impact on the liquid rheology is described on the basis of the temperature-superposition principle and activation theory. The dispersion equation for the waveguide, considered as a thin-walled tube with polymeric solution, is obtained within a quasi-one-dimensional formulation. Results of the study illustrate the influence of temperature on sound propagation in the system.
Abstract: There is an increasing demand for broadband services
in Indonesia. Therefore, the answer is the use of Ka-Band which has
some advantages such as wider bandwidth, the higher transmission
speeds, and smaller size of antenna in the ground. However, rain
attenuation is the primary factor in the degradation of signal at the
Kaband. In this paper, the author will determine whether the Ka-band
frequency can be implemented in Indonesia which has high intensity
of rainfall.
Abstract: Flood routing is used in estimating the travel time and attenuation of flood waves as they move downstream a river or channel. The routing procedure is usually classified as hydrologic or hydraulic. Hydraulic methods utilize the equations of continuity and motion. Kinematic routing, a hydraulic technique was used in routing Asa River at Ilorin. The river is of agricultural and industrial importance to Ilorin, the capital of Kwara State, Nigeria. This paper determines the kinematic parameters of kinematic wave velocity, time step, time required to traverse, weighting factor and change in length. Values obtained were 4.67 m/s, 19 secs, 21 secs, 0.75 and 100 m, respectively. These parameters adequately reflect the watershed and flow characteristics essential for the routing. The synthetic unit hydrograph was developed using the Natural Resources Conservation Service (NRCS) method. 24-hr 10yr, 25yr, 50yr and 100yr storm hydrographs were developed from the unit hydrograph using convolution procedures and the outflow hydrographs were obtained for each of 24-hr 10yr, 25yr, 50yr and 100yr indicating 0.11 m3/s, 0.10 m3/s, 0.10 m3/s and 0.10 m3/s attenuations respectively.
Abstract: In this paper, an analytical study is made for the dynamic behavior of human brain tissue under transient loading. In this analytical model the Mooney-Rivlin constitutive law is coupled with visco-elastic constitutive equations to take into account both the nonlinear and time-dependent mechanical behavior of brain tissue. Five ordinary differential equations representing the relationships of five main parameters (radial stress, circumferential stress, radial strain, circumferential strain, and particle velocity) are obtained by using the characteristic method to transform five partial differential equations (two continuity equations, one motion equation, and two constitutive equations). Analytical expressions of the attenuation properties for spherical wave in brain tissue are analytically derived. Numerical results are obtained based on the five ordinary differential equations. The mechanical responses (particle velocity and stress) of brain are compared at different radii including 5, 6, 10, 15 and 25 mm under four different input conditions. The results illustrate that loading curves types of the particle velocity significantly influences the stress in brain tissue. The understanding of the influence by the input loading cures can be used to reduce the potentially injury to brain under head impact by designing protective structures to control the loading curves types.
Abstract: To develop the useful acoustic environmental
recognition system, the method of estimating 3D-position of a
stationary random acoustic source using bispectral analysis of
4-point detected signals is proposed. The method uses information
about amplitude attenuation and propagation delay extracted from
amplitude ratios and angles of auto- and cross-bispectra of the
detected signals. It is expected that using bispectral analysis affects
less influence of Gaussian noises than using conventional power
spectral one. In this paper, the basic principle of the method is
mentioned first, and its validity and features are considered from
results of the fundamental experiments assumed ideal circumstances.
Abstract: The influence of finite ground conductivity is of great importance in calculating the induced voltages from the radiated electromagnetic fields due to lightning. In this paper, we try to give a comprehensive approach to calculate the impact of the ground on the radiated electromagnetic fields to lightning. The vertical component of lightning electric field is calculated with a reasonable approximation assuming a perfectly conducting ground in case the observation point does not exceed a few kilometers from the lightning channel. However, for distant observation points the radiated vertical component of lightning electric field is attenuated due finitely conducting ground. The attenuation is calculated using the expression elaborated for both low and high frequencies. The horizontal component of the electric field, however, is more affected by a finite conductivity of a ground. Besides, the contribution of the horizontal component of the electric field, to induced voltages on an overhead transmission line, is greater than that of the vertical component. Therefore, the calculation of the horizontal electric field is great concern for the simulation of lightning-induced voltages. For field to transmission lines coupling the ground impedance is calculated for early time behavior and for low frequency range.
Abstract: The simulated mass and spring method evaluation for subway or railways construction and installation systems have a wide application in rail industries. This kind of design should be optimizing all related parameters to reduce the amount of vibration in cities, homelands, historical zones and other critical locations. Finite element method could help us a lot to analysis such applications with an excellent accuracy but always developing some simple, fast and user friendly evaluation method required in subway industrial applications. In addition, process parameter optimization extremely required in railway industries to achieve some optimal design of railways with maximum safety, reliability and performance. Furthermore, it is important to reduce vibrations and further related maintenance costs as well as possible. In this paper a simple but useful simulated mass and spring evaluation system developed for Esfahan subway construction. Besides, some of related recent patent and innovations in rail world industries like Suspension mass tuned vibration reducer, short sleeper vibration attenuation fastener and Airtight track vibration-noise reducing fastener discussed in details.
Abstract: Novel compact expressions for propagation constant (γ) of SWCNT and bundled SWCNTs interconnect, in terms of physical parameters such as length, operating frequency and diameter of CNTs is proposed in this work. These simplified expressions enable physical insight and accurate estimation of signal attenuation level and its phase change at any length for a particular frequency. The proposed expressions are validated against SPICE simulated results of lumped as well as distributed equivalent electrical RLC nets of CNT interconnect. These expressions also help us to evaluate the cut off frequencies of SWCNTs for different interconnect lengths.