Search results for: forced vibrations

Authors: Kambiz Hassanzadeh, Seyedeh Shohreh Ebrahimi, Shahrbanoo Oryan, Arman Rahimmi, Esmael Izadpanah

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Parkinson’s disease is one of the most prevalent neurodegenerative diseases which occurs in elderly. There are convincing evidences that oxidative stress has an important role in both the initiation and progression of Parkinson’s disease. Thymoquinone (TQ) is shown to have antioxidant and anti-inflammatory properties in invitro and invivo studies. It is well documented that TQ acts as a free radical scavenger and prevents the cell damage. Therefore this study aimed to evaluate the effect of TQ on motor and non-motor symptoms in animal model of Parkinson’s disease. Male Wistar rats (10-12 months) received rotenone (1mg/kg/day, sc) to induce Parkinson’s disease model. Pretreatment with TQ (7.5 and 15 mg/kg/day, po) was administered one hour before the rotenone injection. Three motor tests (rotarod, rearing and bar tests) and two non-motor tests (forced swimming and elevated plus maze) were performed for behavioral assessment. Our results indicated that TQ significantly ameliorated the rotenone-induced motor dysfunction in rotarod and rearing tests also it could prevent the non-motor dysfunctions in forced swimming and elevated plus maze tests. In conclusion we found that TQ delayed the Parkinson's disease induction by rotenone and this effect might be related to its proved antioxidant effect.

Keywords: Parkinson's disease, thymoquinone, motor and non-motor symptoms, neurodegenerative disease

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Authors: Saroj Pandey

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COVID-19, declared by the World Health Organization a pandemic (WHO,2020), has created an unprecedented crisis world over endangering the human survival itself. Corona induced lockdowns forced approximately 140 million students of 190 countries at various levels of education from preprimary to higher education to remain confined to their homes. In India, approximately 360 million students were affected by the forced shut down of schools due to the countrywide lockdown in March 2020 and resultant disruption of education. After the initial shock and anxiety the Indian polity and education system bounced back with a number of initiatives, and online education came as a major rescuer for the education system of the country. The distance and online mode of learning that was treated as the poor cousin of conventional mode and often criticized for its quality became the major crusader overnight changing the entire ecosystem of traditional teaching -leaning towards the virtual mode. Teachers who were averse to technology were forced to remodel their educational pedagogies and reorient themselves overnight to use various online platforms such as Zoom, Google meet, and other such platforms to reach the learners. This metamorphosis through ensured students was meaningfully engaged in their studies during the lockdown period but it has its own set of challenges. This paper deals with the government initiatives, and teachers' self-efforts to keep the channel of teaching learning on providing academic and socio emotional support to students during the most difficult period of their life as well as the digital divide between the rich and poor, rural and urban, and boys and girls in India and resultant challenges. It also provides an overview of few significant self-initiatives of teachers to reach their students during the crisis period, who did not have internet and smartphone facilities as well as the initiatives being taken at the government level to address the learning needs and mitigate the learning gaps of learners, bridge the digital divide, strategic planning and upskilling of teachers to overcome the effect of COVID-19 crisis.

Keywords: COVID-19, online education, initiatives, challenges

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Authors: Cheryl-Ann Sarita Boodram

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Historically, the movement of people has been the subject of socio-political and economic regulatory policies which congeal to regulate human mobility and establish geopolitical and spatial identities and borderlands. As migratory practices evolved, so too has the problematization associated with movement, migration and citizenship. The emerging trends have led to active development of immigration technology governing human mobility and the naming of migratory practices. One such named phenomenon is ‘deportation’ or the forced removal of individuals from their adopted country. Deportation, has gained much attention within the human mobility landscape in the past twenty years following the September 2001 terrorist attack on the World Trade Centre in New York. In a reactionary move, several metropolitan countries, including Canada and the United Kingdom enacted or reviewed immigration laws which further enabled the removal of foreign born criminals to the land of their birth in the global south. Existing studies fall short of understanding the multiple textures of the forced returned migration experiences and the social injustices resulting from deportation displacement. This study brings together indigenous research methodologies through the use of participatory action research and social work with returned migrants in Trinidad and Tobago to uncover the experiences of displacement of deported nationals. The study explores the experiences of negotiating life as a ‘stranger’ and how return has influenced the construction of identities of returned nationals. Findings from this study reveal that deportation has led to inequalities and facilitated ‘othering’ of this group within their own country of birth. The study further highlighted that deportation leads to circuits of dispossession, and perpetuates inequalities. This study provides original insights into the way returned migrants negotiate, map and embody ‘strangeness’ and manage their return to a soil they consider unfamiliar and alien.

Keywords: stranger, alien geographies, displacement, deportation, negotiating strangeness, identity, otherness, alien landscapes

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Authors: K. Meera Saheb, K. Krishna Bhaskar

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Complex structures used in many fields of engineering are made up of simple structural elements like beams, plates etc. These structural elements, sometimes carry concentrated masses at discrete points, and when subjected to severe dynamic environment tend to vibrate with large amplitudes. The frequency amplitude relationship is very much essential in determining the response of these structural elements subjected to the dynamic loads. For Timoshenko beams, the effects of shear deformation and rotary inertia are to be considered to evaluate the fundamental linear and nonlinear frequencies. A commonly used method for solving vibration problem is energy method, or a finite element analogue of the same. In the present Coupled Displacement Field method the number of undetermined coefficients is reduced to half when compared to the famous Rayleigh Ritz method, which significantly simplifies the procedure to solve the vibration problem. This is accomplished by using a coupling equation derived from the static equilibrium of the shear flexible structural element. The prime objective of the present paper here is to study, in detail, the effect of a central concentrated mass on the large amplitude free vibrations of uniform shear flexible beams. Accurate closed form expressions for linear frequency parameter for uniform shear flexible beams with a central concentrated mass was developed and the results are presented in digital form.

Keywords: coupled displacement field, coupling equation, large amplitude vibrations, moderately thick plates

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Authors: S. M. Mabandla, P. Loveday, C. Gomes, D. T. Maiga, T. T. Phadi

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Lead zirconate titanate (PZT) piezoelectric ceramics are widely used in ultrasonic applications due to their ability to effectively convert electrical energy into mechanical vibrations and vice versa. This paper presents a study on the behaviour of various combinations of pairs of PZT piezoelectric ceramic materials positioned adjacent to each other with an intermediate gap submerged in water, where one piezoelectric ceramic material is excited by a cyclic electric field with constant frequency and amplitude displacement. The transmitted ultrasonic sound propagates through the medium and is received by the PZT ceramic at the other end, the ultrasonic sound signal amplitude displacement experiences attenuation during propagation due to acoustic impedance. The investigation focuses on understanding the causes of extremely high amplitude displacement attenuation that have been observed in various combinations of piezoelectric ceramic pairs that are submerged in water arranged in a manner stipulated earlier. by examining various combinations of pairs of these piezoelectric ceramics, their physical, electrical, and acoustic properties, and behaviour and attributing them to the observed significant signal attenuation. The experimental setup involves exciting one piezoelectric ceramic material at one end with a burst square cyclic electric field signal of constant frequency, which generates a burst of ultrasonic sound that propagates through the water medium to the adjacent piezoelectric ceramic at the other end. Mechanical vibrations of a PZT piezoelectric ceramic are measured using a double-beam laser Doppler vibrometer to mimic the incident ultrasonic waves generated and received ultrasonic waves on the other end due to mechanical vibrations of a PZT. The measured ultrasonic sound wave signals are continuously compared to the applied cyclic electric field at both ends. The impedance matching networks are continuously tuned at both ends to eliminate electromechanical impedance mismatch to improve ultrasonic transmission and reception. The study delves into various physical, electrical, and acoustic properties of the PZT piezoelectric ceramics, such as the electromechanical coupling factor, acoustic coupling, and elasticity, among others. These properties are analyzed to identify potential factors contributing to the unusually high acoustic impedance in the water medium between the ceramics. Additionally, impedance-matching networks are investigated at both ends to offset the high signal attenuation and improve overall system performance. The findings will be reported in this paper.

Keywords: acoustic impedance, impedance mismatch, piezoelectric ceramics, ultrasonic sound

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Authors: Haithem Elderrat, Huw Davies, Emmanuel Brousseau

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Elastomeric polymer foam has been used widely in the automotive industry, especially for isolating unwanted vibrations. Such material is able to absorb unwanted vibration due to its combination of elastic and viscous properties. However, the ‘creep effect’, poor stress distribution and susceptibility to high temperatures are the main disadvantages of such a system. In this study, improvements in the performance of elastomeric foam as a vibration isolator were investigated using the concept of Foam Filled Fluid (FFFluid). In FFFluid devices, the foam takes the form of capsule shapes, and is mixed with viscous fluid, while the mixture is contained in a closed vessel. When the FFFluid isolator is affected by vibrations, energy is absorbed, due to the elastic strain of the foam. As the foam is compressed, there is also movement of the fluid, which contributes to further energy absorption as the fluid shears. Also, and dependent on the design adopted, the packaging could also attenuate vibration through energy absorption via friction and/or elastic strain. The present study focuses on the advantages of the FFFluid concept over the dry polymeric foam in the role of vibration isolation. This comparative study between the performance of dry foam and the FFFluid was made according to experimental procedures. The paper concludes by evaluating the performance of the FFFluid isolator in the suspension system of a light vehicle. One outcome of this research is that the FFFluid may preferable over elastomer isolators in certain applications, as it enables a reduction in the effects of high temperatures and of ‘creep effects’, thereby increasing the reliability and load distribution. The stiffness coefficient of the system has increased about 60% by using an FFFluid sample. The technology represented by the FFFluid is therefore considered by this research suitable for application in the suspension system of a light vehicle.

Keywords: FFFluid, dry foam, anti-vibration devices, elastomeric polymer foam

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Authors: M. Ali Lotfollahi Yaghin, M. Reza Bagerzadeh Karimi, Ali Rahmani, V. Sadeghi Balkanlou

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Structural engineers have long been trying to develop solutions using the full potential of its composing materials. Therefore, there is no doubt that the structural solution progress is directly related to an increase in materials science knowledge. These efforts in conjunction with up-to-date modern construction techniques have led to an extensive use of composite floors in large span structures. On the other hand, the competitive trends of the world market have long been forcing structural engineers to develop minimum weight and labour cost solutions. A direct consequence of this new design trend is a considerable increase in problems related to unwanted floor vibrations. For this reason, the structural floors systems become vulnerable to excessive vibrations produced by impacts such as human rhythmic activities. The main objective of this paper is to present an analysis methodology for the evaluation of the composite floors human comfort. This procedure takes into account a more realistic loading model developed to incorporate the dynamic effects induced by human walking. The investigated structural models were based on various composite floors, with main spans varying from 5 to 10 m. based on an extensive parametric study the composite floors dynamic response, in terms of peak accelerations, was obtained and compared to the limiting values proposed by several authors and design standards. This strategy was adopted to provide a more realistic evaluation for this type of structure when subjected to vibration due to human walking.

Keywords: vibration, resonance, composite floors, people’s rhythmic movement, dynamic analysis, Abaqus software

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Authors: S. A. Alotaibi, M. A. Al-Ajmi

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This work introduces a new concept for controlling the mechanical vibrations via variable stiffness coil spring. The concept relies on fitting a screw though the spring to change the number of active spring coils. A prototype has been built and tested with promising results toward an innovation in the field of vibration control.

Keywords: variable stiffness, coil spring, vibration control, computer science

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Authors: Andrea Tonoli, Nicola Amati, Maria Cavatorta, Reza Mirsanei, Behzad Mozaffari, Hamed Ahani, Akbar Karamihafshejani, Mohammad Ghazivakili, Mohammad Abuabiah

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The vibrations transmitted to the drivers and passengers through vehicle seat seriously effect on the level of their attention, fatigue and physical health and reduce the comfort and efficiency of the occupants. Recently, some researchers have focused on vibrations at low excitation frequency(0.5-5 Hz) which are considered to be the main risk factors for lumbar part of the backbone but they were not applicable to A and B-segment cars regarding to the size and weight. A semi-active system with two symmetric negative stiffness structures (NSS) in parallel to a positive stiffness structure and actuators has been proposed to attenuate low frequency excitation and makes system flexible regarding to different weight of passengers which is applicable for A and B-Segment cars. Here, the 3 degree of freedom system is considered, dynamic equation clearly is presented, then simulated in MATLAB in order to analysis of performance of the system. The design procedure is derived so that the resonance peak of frequency–response curve shift to the left, the isolating range is increased and especially, the peak of the frequency–response curve is minimized. According to ISO standard different class of road profile as an input is applied to the system to evaluate the performance of the system. To evaluate comfort issues, we extract the RMS value of the vertical acceleration acting on the passenger's body. Then apply the band-pass filter, which takes into account the human sensitivity to acceleration. According to ISO, this weighted acceleration is lower than 0.315 m/s^2, so the ride is considered as comfortable.

Keywords: low frequency excitation, negative stiffness, seat vehicle, vibration isolation

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Authors: Fernández-Brito David, Lopez-Medina Javier Alonso, Murillo-Bracamontes Eduardo Antonio, Palomino-Ovando Martha Alicia, Gervacio-Arciniega José Juan

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Magnetic Force Microscopy (MFM) is an Atomic Force Microscopy (AFM) technique that characterizes, at a nanometric scale, the magnetic properties of ferromagnetic materials. Conventional MFM works by scanning in two different AFM modes. The first one is tapping mode, in which the cantilever has short-range force interactions with the sample, with the purpose to obtain the topography. Then, the lift AFM mode starts, raising the cantilever to maintain a fixed distance between the tip and the surface of the sample, only interacting with the magnetic field forces of the sample, which are long-ranged. In recent years, there have been attempts to improve the MFM technique. Bimodal MFM was first theoretically developed and later experimentally proven. In bimodal MFM, the AFM internal piezoelectric is used to cause the cantilever oscillations in two resonance modes simultaneously, the first mode detects the topography, while the second is more sensitive to the magnetic forces between the tip and the sample. However, it has been proven that the cantilever vibrations induced by the internal AFM piezoelectric ceramic are not optimal, affecting the bimodal MFM characterizations. Moreover, the Secondary Resonance Magnetic Force Microscopy (SR-MFM) was developed. In this technique, a coil located below the sample generates an external magnetic field. This alternating magnetic field excites the cantilever at a second frequency to apply the Bimodal MFM mode. Nonetheless, for ferromagnetic materials with a low coercive field, the external field used in SR-MFM technique can modify the magnetic domains of the sample. In this work, a Hybrid Bimodal MFM (HB-MFM) technique is proposed. In HB-MFM, the bimodal MFM is used, but the first resonance frequency of the cantilever is induced by the magnetic field of the ferromagnetic sample due to its vibrations caused by a piezoelectric element placed under the sample. The advantages of this new technique are demonstrated through the preliminary results obtained by HB-MFM on a hard disk sample. Additionally, traditional two pass MFM and HB-MFM measurements were compared.

Keywords: magnetic force microscopy, atomic force microscopy, magnetism, bimodal MFM

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Authors: Bushra Nabi, Saleha Rehman, Sanjula Baboota, Javed Ali

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Aim: The objective of research undertaken is analytical method validation (HPLC method) of an anti-HIV drug Elvitegravir (EVG). Additionally carrying out the forced degradation studies of the drug under different stress conditions to determine its stability. It is envisaged in order to determine the suitable technique for drug estimation, which would be employed in further research. Furthermore, comparative pharmacokinetic profile of the drug from lipid architectonics and drug suspension would be obtained post oral administration. Method: Lipid Architectonics (LA) of EVR was formulated using probe sonication technique and optimized using QbD (Box-Behnken design). For the estimation of drug during further analysis HPLC method has been validation on the parameters (Linearity, Precision, Accuracy, Robustness) and Limit of Detection (LOD) and Limit of Quantification (LOQ) has been determined. Furthermore, HPLC quantification of forced degradation studies was carried out under different stress conditions (acid induced, base induced, oxidative, photolytic and thermal). For pharmacokinetic (PK) study, Albino Wistar rats were used weighing between 200-250g. Different formulations were given per oral route, and blood was collected at designated time intervals. A plasma concentration profile over time was plotted from which the following parameters were determined:

Keywords: AIDS, Elvitegravir, HPLC, nanostructured lipid carriers, pharmacokinetics

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Authors: M. Khalid, W. Rashmi, L. L. Kwan

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This work provides an overview on the experimental and numerical simulations of various nanofluids and their flow and heat transfer behavior. It was further extended to study the effect of nanoparticle concentration, fluid flow rates and thermo-physical properties on the heat transfer enhancement of Al2O3/water nanofluid in a turbulent flow circular conduit using ANSYS FLUENT™ 14.0. Single-phase approximation (homogeneous model) and two-phase (mixture and Eulerian) models were used to simulate the nanofluid flow behavior in the 3-D horizontal pipe. The numerical results were further validated with experimental correlations reported in the literature. It was found that heat transfer of nanofluids increases with increasing particle volume concentration and Reynolds number, respectively. Results showed good agreement (~9% deviation) with the experimental correlations, especially for a single-phase model with constant properties. Among two-phase models, mixture model (~14% deviation) showed better prediction compared to Eulerian-dispersed model (~18% deviation) when temperature independent properties were used. Non-drag forces were also employed in the Eulerian two-phase model. However, the two-phase mixture model with temperature dependent nanofluid properties gave slightly closer agreement (~12% deviation).

Keywords: nanofluid, CFD, heat transfer, forced convection, circular conduit

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Authors: Uluhan Berk Ondul

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This article aims to shed light on the new stage of transitional justice in Argentina through examining the representations of the 2x1 decision of the Supreme Court and Santiago Maldonado’s Disappearance in the newspaper, La Nación. The two events hold the key to understanding Argentina’s journey since return to democracy as they are about the same crimes of the dictatorship, namely, the forced disappearance of civilians and the subsequent impunity that follows. In the case of a convicted torturer, The Supreme Court of Argentina ruled on 3rd of May 2017 that the days spent in preventive detention after two years should be counted double for the overall sentence. This court decision was met with severe resistance from the members of the parliament as well as the human rights movement. The second item on the list still continues and divides the country into two camps: (1) those who think that the police force has committed another act of forced disappearance in the case of activist Santiago Maldonado and (2) the others who blame the peronistas (the party and supporters of the ex-president Cristina Fernandez de Kirchner) of using this subject as a means to score political points. As a newspaper known for its proximity to the current administration, La Nación offers an insight to the direction of the country and also demonstrates how the neoliberal mindset works. The results of the study show that the transitional justice process in Argentina is far from being complete as the Promise of Nunca Más is still not a shared value but a political statement.

Keywords: Argentina, Fallo 2x1, impunity, Santiago Maldonado, transitional justice

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Authors: M. Inmaculada Alvarez-Fernández, Celestino González-Nicieza, M. Belén Prendes-Gero, Fernando López-Gayarre

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Among many factors affecting the stability of mining excavations, rock-bursts and tremors play a special role. These dynamic loads occur practically always and have different sources of generation. The most important of them is the commonly used mining technique, which disintegrates a certain area of the rock mass not only in the area of the planned mining, but also creates waves that significantly exceed this area affecting the structural elements. In this work it is analysed the consequences of dynamic loads over the structural elements in an underground room and pillar mine to avoid roof instabilities. With this end, dynamic loads were evaluated through in situ and laboratory tests and simulated with numerical modelling. Initially, the geotechnical characterization of all materials was carried out by mean of large-scale tests. Then, drill holes were done on the roof of the mine and were monitored to determine possible discontinuities in it. Three seismic stations and a triaxial accelerometer were employed to measure the vibrations from blasting tests, establish the dynamic behaviour of roof and pillars and develop the transmission laws. At last, computer simulations by FLAC3D software were done to check the effect of vibrations on the stability of the roofs. The study shows that in-situ tests have a greater reliability than laboratory samples because of eliminating the effect of heterogeneities, that the pillars work decreasing the amplitude of the vibration around them, and that the tensile strength of a beam and depending on its span is overcome with waves in phase and delayed. The obtained transmission law allows designing a blasting which guarantees safety and prevents the risk of future failures.

Keywords: dynamic modelling, long term instability risks, room and pillar, seismic collapse

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Authors: Razmik Atabekyan, V. Atabekyan

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This article discusses a new alternative method for determination of seismic loads on buildings, based on resistance of structures to deformations of vibrations. The basic principles for determining seismic loads by spectral method were developed in 40… 50ies of the last century and further have been improved to pursuit true assessments of seismic effects. The base of the existing methods to determine seismic loads is response spectrum or dynamicity coefficient β (norms of RF), which are not definitively established. To this day there is no single, universal method for the determination of seismic loads and when trying to apply the norms of different countries, significant discrepancies between the results are obtained. On the other hand there is a contradiction of the results of macro seismic surveys of strong earthquakes with the principle of the calculation based on accelerations. It is well-known, on soft soils there is an increase of destructions (mainly due to large displacements), even though the accelerations decreases. Obviously, the seismic impacts are transmitted to the building through foundation, but paradoxically, the existing methods do not even include foundation data. Meanwhile acceleration of foundation of the building can differ several times from the acceleration of the ground. During earthquakes each building has its own peculiarities of behavior, depending on the interaction between the soil and the foundations, their dynamic characteristics and many other factors. In this paper we consider a new, alternative method of determining the seismic loads on buildings, without the use of response spectrum. The following main conclusions: 1) Seismic loads are revealed at the foundation level, which leads to redistribution and reduction of seismic loads on structures. 2) The proposed method is universal and allows determine the seismic loads without the use of response spectrum and any implicit coefficients. 3) The possibility of taking into account important factors such as the strength characteristics of the soils, the size of the foundation, the angle of incidence of the seismic ray and others. 4) Existing methods can adequately determine the seismic loads on buildings only for first form of vibrations, at an average soil conditions.

Keywords: seismic loads, response spectrum, dynamic characteristics of buildings, momentum

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Authors: Ataollah Rabiee1, Amir Hossein Kamalinia, Alireza Atf

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One of the most important issues in the design of nuclear fusion power plants is the heat removal from the hottest region at the diverter. Various methods could be employed in order to improve the heat transfer efficiency, such as generating turbulent flow and injection of nanoparticles in the host fluid. In the current study, Water/AL₂O₃ nanofluid forced swirl flow boiling has been investigated by using a homogeneous thermophysical model within the Eulerian-Eulerian framework through a twisted tape tube, and the boiling phenomenon was modeled using the Rensselaer Polytechnic Institute (RPI) approach. In addition to comparing the results with the experimental data and their reasonable agreement, it was evidenced that higher flow mixing results in more uniform bulk temperature and lower wall temperature along the twisted tape tube. The presence of AL₂O₃ nanoparticles in the boiling flow field showed that increasing the nanoparticle concentration leads to a reduced vapor volume fraction and wall temperature. The Computational fluid dynamics (CFD) results show that the average heat transfer coefficient in the tube increases both by increasing the nanoparticle concentration and the insertion of twisted tape, which significantly affects the thermal field of the boiling flow.

Keywords: nanoparticle, boiling, CFD, two phase flow, alumina, ITER

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Authors: Ali Etemadi, Claudia Fernanda Yasar

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Elevated water storage tank structures (EWSTs) are high elevated-ponderous structural systems and very vulnerable to seismic vibrations. In past earthquake events, many of these structures exhibit poor performance and experienced severe damage. The dynamic analysis of the EWSTs under earthquake loads is, therefore, of significant importance for the design of the structure and a key issue for the development of modern methods, such as active control design. In this study, a reduced model of the EWSTs is explained, which is based on a tuned mass damper model (TMD). Vibration analysis of a structure under seismic excitation is presented and then used to propose an active vibration controller. MATLAB/Simulink is employed for dynamic analysis of the system and control of the seismic response. A single degree of freedom (SDOF) and two degree of freedom (2DOF) models of ELSTs are going to be used to study the concept of active vibration control. Lab-scale experimental models similar to pendulum are applied to suppress vibrations in ELST under seismic excitation. One of the most important phenomena in liquid storage tanks is the oscillation of fluid due to the movements of the tank body because of its base motions during an earthquake. Simulation results illustrate that the EWSTs vibration can be reduced by means of an input shaping technique that takes into account the dominant mode shape of the structure. Simulations with which to guide many of our designs are presented in detail. A simple and effective real-time control for seismic vibration damping can be, therefore, design and built-in practice.

Keywords: elevated water storage tank, tuned mass damper model, real time control, shaping control, seismic vibration control, the laplace transform

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Authors: Iyd Eqqab Maree, Habil Jurgen Bast

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Vibration control of machines and structures incorporating viscoelastic materials in suitable arrangement is an important aspect of investigation. The use of viscoelastic layers constrained between elastic layers is known to be effective for damping of flexural vibrations of structures over a wide range of frequencies. The energy dissipated in these arrangements is due to shear deformation in the viscoelastic layers, which occurs due to flexural vibration of the structures. Multilayered cantilever sandwich beam like structures can be used in aircrafts and other applications such as robot arms for effective vibration control. These members may experience parametric instability when subjected to time dependant forces. The theory of dynamic stability of elastic systems deals with the study of vibrations induced by pulsating loads that are parametric with respect to certain forms of deformation. The purpose of the present work is to investigate the dynamic stability of a three layered symmetric sandwich beam (Drone Aircraft wings ) subjected to an end periodic axial force . Equations of motion are derived using finite element method (MATLAB software). It is observed that with increase in core thickness parameter fundamental buckling load increases. The fundamental resonant frequency and second mode frequency parameter also increase with increase in core thickness parameter. Fundamental loss factor and second mode loss factor also increase with increase in core thickness parameter. Increase in core thickness parameter enhances the stability of the beam. With increase in core loss factor also the stability of the beam enhances. There is a very good agreement of the experimental results with the theoretical findings.

Keywords: steel cantilever beam, viscoelastic material core, loss factor, transition region, MATLAB R2011a

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Authors: Bayram Sahin, Baris Gezdirici, Murat Ceylan, Ibrahim Ates

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In this experimental study, the effects of heat transfer and flow characteristics on lattice geometric heat sinks, where high rates of heat removal are required, were investigated. The design parameters were Reynolds number, the height of heat sink (H), horizontal (Sy) and vertical (Sx) distances between heat sinks. In the experiments, the Reynolds number ranged from 4000 to 20000; heat sink heights were (H) 20 mm and 40 mm; the distances (Sy) between the heat sinks in the flow direction were45 mm, 32 mm, 23.3 mm; the distances (Sx) between the heat sinks perpendicular to the flow direction were selected to be 23.3 mm, 12.5 mm and 6 mm. A total of 90 experiments were conducted and the maximum Nusselt number and minimum friction coefficient were targeted. Experimental results have shown that heat sinks in lattice geometry have a significant effect on heat transfer enhancement. Under the different experimental conditions, the highest increase in Nusselt number was 283% while the lowest increase was calculated as 66% as compared with the straight channel results. The lowest increase in the friction factor was also obtained as 173% according to the straight channel results. It is seen that the increase in heat sink height and flow velocity increased the level of turbulence in the channel, leading to higher Nusselt number and friction factor values.

Keywords: forced convection, heat transfer enhancement, lattice geometric heat sinks, pressure drop

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Authors: Manal Alhazmi, Artem Mishchenko

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A molecular fluids' behavior and interaction with other materials at the nanoscale is a complex process. Nanoscale fluids behave so differently than macroscale fluids and interact with other materials in unique ways. It is, therefore, feasible to understand the molecular behavior of H₂O in such two-dimensional nanoscale systems by studying (CaSO4-2H2O), commonly known as gypsum. In the present study, spectroscopic measurements on a 2D structure of exfoliated gypsum crystals are carried out by Raman and IR spectroscopy. An array of gypsum flakes with thicknesses ranging from 8nm to 100nm were observed and analyzed for their Raman and IR spectrum. Water molecules stretching modes spectra lines were also measured and observed in nanoscale gypsum flakes and compared with those of bulk crystals. CaSO4-2H2O crystals have Raman and infrared bands at 3341 cm-1 resulting from the weak hydrogen bonds between the water molecules. This internal vibration of water molecules, together with external vibrations with other atoms, are responsible for these bands. There is a shift of about 70 cm-1 In the peak position of thin flakes with respect to the bulk crystal, which is a result of the different atomic arrangement from bulk to thin flake on the nano scale. An additional peak was observed in Raman spectra around 2910-3137 cm⁻¹ in thin flakes but is missing in bulk crystal. This additional peak is attributed to a combined mode of water internal (stretching mode at 3394cm⁻¹) and external vibrations. In addition to Raman and infra- red analysis of gypsum 2D structure, electrical measurements were conducted to reveal the water molecules transport behavior in such systems. Electrical capacitance of the fabricated device is measured and found to be (0.0686 *10-12) F, and the calculated dielectric constant (ε) is (12.26).

Keywords: gypsum, infra-red spectroscopy, raman spectroscopy, H₂O behavior

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Authors: Liliia N. Butymova, Vladimir Y. Modorsky, Nikolai A. Shevelev

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Prediction of vibration processes in gas transmittal units (GTU) is an urgent problem. Despite numerous scientific publications on the problem of vibrations in general, there are not enough works concerning FSI-modeling interaction processes between several deformable blades in gas-dynamic flow. Since it is very difficult to solve the problem in full scope, with all factors considered, a unidirectional dynamic coupled 1FSI model is suggested for use at the first stage, which would include, from symmetry considerations, two blades, which might be considered as the first stage of solving more general bidirectional problem. ANSYS CFX programmed multi-processor was chosen as a numerical computation tool. The problem was solved on PNRPU high-capacity computer complex. At the first stage of the study, blades were believed oscillating with the same frequency, although oscillation phases could be equal and could be different. At that non-stationary gas-dynamic forces distribution over the blades surfaces is calculated in run of simulation experiment. Oscillations in the “gas — structure” dynamic system are assumed to increase if the resultant of these gas-dynamic forces is in-phase with blade oscillation, and phase shift (φ=0). Provided these oscillation occur with phase shift, then oscillations might increase or decrease, depending on the phase shift value. The most important results are as follows: the angle of phase shift in inter-blade oscillation and the gas-dynamic force depends on the flow velocity, the specific inter-blade gap, and the shaft rotation speed; a phase shift in oscillation of adjacent blades does not always correspond to phase shift of gas-dynamic forces affecting the blades. Thus, it was discovered, that asynchronous oscillation of blades might cause either attenuation or intensification of oscillation. It was revealed that clocking effect might depend not only on the mutual circumferential displacement of blade rows and the gap between the blades, but also on the blade dynamic deformation nature.

Keywords: aeroelasticity, ANSYS CFX, oscillation, phase shift, clocking effect, vibrations

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Authors: Sahin Yakut, H. Kemal Ulutas, Deniz Deger

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Plasma Assisted Physical Vapor Deposition (PAPVD) method used to produce Poly(ethylene oxide) (pPEO) thin films. Depositions were progressed at various plasma discharge powers as 0, 2, 5 and 30 W for pPEO at 500nm film thicknesses. The capacitance and dielectric dissipation of the thin films were measured at 0,1-107 Hz frequency range and 173-353 K temperature range by an impedance analyzer. Then, alternative conductivity (σac) and activation energies were derived from capacitance and dielectric dissipation. σac of conventional PEO (PEO precursor) was measured to determine the effect of plasma discharge. Differences were observed between the alternative conductivity of PEO’s and pPEO’s depending on plasma discharge power. By this purpose, structural characterization techniques such as Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared Spectroscopy (FT-IR) were applied on pPEO thin films. Structural analysis showed that density of crosslinking is plasma power dependent. The crosslinking density increases with increasing plasma discharge power and this increase is displayed as increasing dynamic glass transition temperatures at DSC results. Also, shifting of frequencies of some type of bond vibrations, belonging to bond vibrations produced after fragmentation because of plasma discharge, were observed at FTIR results. The dynamic glass transition temperatures obtained from alternative conductivity results for pPEO consistent with the results of DSC. Activation energies exhibit Arrhenius behavior. Activation energies decrease with increasing plasma discharge power. This behavior supports the suggestion expressing that long polymer chains and long oligomers are fragmented into smaller oligomers or radicals.

Keywords: activation energy, dielectric spectroscopy, organic thin films, plasma polymer

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Authors: Zhao Bo

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The TiO2-Na2SO3 and SiO2-Na2SO3 nano-fluids were prepared using ultrasonic dispertion method without any surfactant addition to study the influence of nano-fluids on the mass transfer during forced sulfite oxidation in a thermostatic stirred tank, and the kinetic viscosity of nano-fluids was measured. The influence of temperature (30 ℃ ~ 50 ℃), solid loading of fine particle (0 Kg/m³~1.0 Kg/m³), stirring speed (50 r/min ~ 400 r/min), and particle size (10 nm~100 nm) on the average oxygen absorption rate were investigated in detail. Both TiO2 nano-particles and SiO2 nano-particles could remarkably improve the gas-liquid mass transfer. Oxygen absorption enhancement factor increases with the increase of solid loading of nano-particles to a critical value and then decreases with further increase of solid loading under 30℃. Oxygen absorption rate together with absorption enhancement factor increases with stirring speed. However, oxygen absorption enhancement factor decreases with the increase of temperature due to aggregation of nano-particles. Further inherent relationship between particle size, loading, surface area, viscosity, stirring speed, temperature, adsorption, desorption, and mass transfer was discussed in depth by analyzing the interaction mechanism.

Keywords: fine particles, nano-fluid, mass transfer enhancement, solid loading

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Authors: David Ugalde, Arturo Castillo, Leopoldo Breschi

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The Tuned Mass Dampers (TMDs) are an effective system for mitigating vibrations in building structures. These dampers have traditionally focused on the protection of high-rise buildings against earthquakes and wind loads. The Camara Chilena de la Construction (CChC) building, built in 2018 in Santiago, Chile, is a 21-story RC wall building equipped with a 150-ton TMD and instrumented with six permanent accelerometers, offering an opportunity to monitor the dynamic response of this damped structure. This paper presents the system identification of the CChC building using power spectral density plots of ambient vibration and two seismic events (5.5 Mw and 6.7 Mw). Linear models of the building with and without the TMD are used to compute the theoretical natural periods through modal analysis and simulate the response of the building through response history analysis. Results show that natural periods obtained from both ambient vibrations and earthquake records are quite similar to the theoretical periods given by the modal analysis of the building model. Some of the experimental periods are noticeable by simple inspection of the earthquake records. The accelerometers in the first story better captured the modes related to the building podium while the upper accelerometers clearly captured the modes related to the tower. The earthquake simulation showed smaller accelerations in the model with TMD that are similar to that measured by the accelerometers. It is concluded that the system identification through power spectral density shows consistency with the expected dynamic properties. The structural health monitoring of the CChC building confirms the advantages of seismic protection technologies such as TMDs in seismic prone areas.

Keywords: system identification, tuned mass damper, wall buildings, seismic protection

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Authors: Yuan-Ching Chiang, Chien-Yeh Hsu, Chen Chih-Hao, Sih-Li Chen

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The p-n junction temperature of LEDs directly influences their operating life and luminous efficiency. An excessively high p-n junction temperature minimizes the output flux of LEDs, decreasing their brightness and influencing the photon wavelength; consequently, the operating life of LEDs decreases and their luminous output changes. The maximum limit of the p-n junction temperature of LEDs is approximately 120 °C. The purpose of this research was to devise an approach for dissipating heat generated in a confined space when LEDs operate at low temperatures to reduce light decay. The cooling mode of existing commercial LED lights can be divided into natural- and forced convection cooling. In natural convection cooling, the volume of LED encapsulants must be increased by adding more fins to increase the cooling area. However, this causes difficulties in achieving efficient LED lighting at high power. Compared with forced convection cooling, heat transfer through water convection is associated with a higher heat transfer coefficient per unit area; therefore, we dissipated heat by using a closed loop water cooling system. Nevertheless, cooling water exposed to air can be easily influenced by environmental factors. Thus, we incorporated a ground heat exchanger into the water cooling system to minimize the influence of air on cooling water and then observed the relationship between the amounts of heat dissipated through the ground and LED efficiency.

Keywords: helical ground heat exchanger, high power LED, ground source cooling system, heat dissipation

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Authors: D: Gupta, M. Radhakrishnan, Y. Kurhe, D. Thangaraj

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Depression is among the leading causes of death worldwide. The current pharmacotherapy is associated with poor compliance, resistance and relapse, which necessitate the development of novel compounds with better efficacy. The present study designed and synthesized EQC-34 (N-cyclohexyl-3-ethoxyquinoxalin-2-carboxamide) as novel serotonin type-3 (5HT3) antagonist and evaluated its antidepressant-like effects using neurobehavioral mouse model. 5HT3 antagonism (as pA2 value) was determined on the longitudinal smooth muscle of guinea-pig ileum against 2-methyl-5HT (a 5HT3 agonist). The doses were calculated by dose response of basal locomotor activity. Consequently, effects of EQC-34 on neurobehavioral parameters were measured in forced swim (FST) and tail suspension test (TST). The possible mechanism was estimated by interaction study with fluoxetine (a selective serotonin reuptake inhibitor) and mCPBG (1-(m-chlorophenyl)-biguanide, a selective 5HT3 agonist), and confirmed by potentiation of head twitch response by 5hydroxy-L-tryptophan (5HTP). EQC-34 (1-4 mg/kg, i.p.) produced significant decreased behavioral despair effects in FST and TST. It potentiated fluoxetine response, while mCPBG reduced EQC-34 activity in FST. Further, EQC-34 potentiated 5HTP induced head twitch response. EQC-34 revealed potential antidepressant-like effects, which may involve 5HT3 receptor mediated facilitation of 5HT neurotransmission, thereby reversing the pathological deficiency of monoamines (5HT) observed in depression. Thus, it may be further investigated as promising agent to improve therapeutics of depression.

Keywords: depression, forced swim test, 5HT3 receptor antagonist, serotonin

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Authors: Yasser Mahmoudi, Nader Karimi

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The present work investigates numerically the effect of thermal radiation from the solid phase on the rate of heat transfer inside a porous medium. Forced convection heat transfer process within a pipe filled with a porous media is considered. The Darcy-Brinkman-Forchheimer model is utilized to represent the fluid transport within the porous medium. A local thermal non-equilibrium (LTNE), two-equation model is used to represent the energy transport for the solid and fluid phases. The radiative heat transfer equation is solved by discrete ordinate method (DOM) to compute the radiative heat flux in the porous medium. Two primary approaches (models A and B) are used to represent the boundary conditions for constant wall heat flux. The effects of radiative heat transfer on the Nusselt numbers of the two phases are examined by comparing the results obtained by the application of models A and B. The fluid Nusselt numbers calculated by the application of models A and B show that the Nusselt number obtained by model A for the radiative case is higher than those predicted for the non-radiative case. However, for model B the fluid Nusselt numbers obtained for the radiative and non-radiative cases are similar.

Keywords: porous media, local thermal non-equilibrium, forced convection heat transfer, thermal radiation, Discrete Ordinate Method (DOM)

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Authors: Usman Abubakar, Xiaoyuan Wang, Sayyed Haleem Shah, Sadiq Ur Rahman, Rabiu Saleh Zakariyya

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High-speed Permanent magnet synchronous machine (HSPMSM) uses in different industrial applications like blowers, compressors as a result of its superb performance. Nevertheless, the over-temperature rise of both winding and PM is one of their substantial problem for a high-power HSPMSM, which affects its lifespan and performance. According to the literature, HSPMSM with a Hybrid cooling configuration has a much lower temperature rise than non-hybrid cooling. This paper presents the design 185kW, 26K rpm with two different cooling configurations, i.e., hybrid cooling configuration (forced air and housing spiral water jacket) and non-hybrid (forced air cooling assisted with winding’s potting material and sleeve’s material) to enhance the heat dissipation of winding and PM respectively. Firstly, the machine’s electromagnetic design is conducted by the finite element method to accurately account for machine losses. Then machine’s cooling configurations are introduced, and their effectiveness is validated by lumped parameter thermal network (LPTN). Investigation shows that using potting, sleeve materials to assist non-hybrid cooling configuration makes the machine’s winding and PM temperature closer to hybrid cooling configuration. Therefore, the machine with non-hybrid cooling is prototyped and tested due to its simplicity, lower energy consumption and can still maintain the lifespan and performance of the HSPMSM.

Keywords: airflow network, axial ventilation, high-speed PMSM, thermal network

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Authors: Elvis Enowbeyang Tarkang

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Background: Since students in high schools in Cameroon fall within the age group hardest hit by HIV/AIDS, it is assumed that these students might be exposed to sexual risk behaviours. Sexual risk behaviours include engaging in unprotected sexual intercourse, early sexual debut, multiple sexual partners and coerced or forced sex, and these behaviours might predispose youth to HIV transmission. However, little has been explored on the sexual risk behaviours of high school learners in Cameroon. This study aimed at examining the sexual risk behaviours of high school students in an urban town of Cameroon. Method: A quantitative cross sectional design was adopted, using a self-administered questionnaire to collect data from a disproportional stratified simple random sample of 480 (240 male and 240 female) grade 10 to grade 12 students from two participating secondary school in Limbe in the Southwest region of Cameroon August 2014. Descriptive and Chi square statistics were calculated using statistical Package for Social Sciences (SPSS) version 20 software program at the level 0.05. Results: Majority of the respondents, 63.4% reported being sexually active, of whom only 33.2% used condoms consistently. Up to 37% of the sexually active respondents had multiple sexual partners in the past one year before the study, while 23% had multiple sexual partners during the study period. The mean age of first sex was 15.4 years. Among Christians, Pentecostals, 17 (58.6%) were more likely to have experienced sexual coercion than non-Pentecostals, 111 (42.2%) (p= 0.000). Christians, 41 (10.3%) were more likely to have been forced into first sex than Muslims, 0 (0.0%); while among the Christians, Pentecostals, 6 (15.0%) were more likely to have been forced into first sex than non-Pentecostals, 35 (10.9%) (p=0.004). Among the Christians, Pentecostals, 16 (66.7%) were more likely to have experienced sex by age 16 years than non-Pentecostals, 125 (64.1%) (p= 0.000). Students who lived in rented places, 32 (22.7%) were more likely to have had multiple sexual partners than those who lived in their parents’ houses, 35 (18.1%) (p= 0.000). Males, 36 (16.0%) were likely to have had multiple concurrent sexual partners than females, 14 (6.0%) (p=0.002). Students who used condoms consistently, 25 (33.3%) were more likely to have a higher perception of risk of contracting HIV than those who did not use condoms consistently, 38 (29.9%) (p=0.002). Students who lived in their parents’ houses, 35 (35.4%) were more likely to use condoms consistently during sex, than those who lived in rented places, 31 (29.8%) (p=0.021). Students who passed their examinations, 57 (30.9%) were more likely to have used condoms consistently than those with low academic profiles, 24 (27.9%) (p= 0.034). Conclusions and Recommendations: Gender, lack of parental control, religion, academic profile, poverty, place of residence and perception of risk of HIV infection were the main factors associated with sexual risk behaviours among students in urban Cameroon. The findings indicate that sexual risk behaviours exist among high school students in Limbe urban town of Cameroon. There is need for campaigns and interventions to bring about sexual behaviour change.

Keywords: Cameroon, high school students, HIV/AIDS, Limbe urban town, sexual risk behaviours

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Authors: J. Leige Lopes, L. Aparecida Bastos, R. Monteiro da Silva

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The objective of this paper is to study the work of children and adolescents and the vicious circle of poverty from the perspective of Guinar Myrdal’s Theory of Circular Cumulative Causation. The objective is to show that if a person starts working in the juvenile phase of life they will be classified as poor or extremely poor when they are adult, which can to be observed in the case of Brazil, more specifically in the north and northeast. To do this, the methodology used was statistical and econometric analysis by applying a probit model. The main results show that: if people reside in the northeastern region of Brazil, and if they have a low educational level and if they start their professional life before the age 18, they will increase the likelihood that they will be poor or extremely poor. There is a consensus in the literature that one of the causes of the intergenerational transmission of poverty is related to child labor, this because when one starts their professional life while still in the toddler or adolescence stages of life, they end up sacrificing their studies. Because of their low level of education, children or adolescents are forced to perform low-paid functions and abandon school, becoming in the future, people who will be classified as poor or extremely poor. As a result of poverty, parents may be forced to send their children out to work when they are young, so that in the future they will also become poor adults, a process that is characterized as the "vicious circle of poverty."

Keywords: children, adolescents, Gunnar Myrdal, poverty, vicious circle

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