324 research outputs found
Editorial
No full textCorresponding Author: Masoud Mirzaei
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Background data for: "The instantaneous structure of a turbulent wall-bounded flow influenced by freestream turbulence: streamwise evolution"
No full textThis data set contains planar Particle Image Velocimetry measurement fields for the experiments described in the article titled "The instantaneous structure of a turbulent wall-bounded flow influenced by freestream turbulence: streamwise evolution" (doi:10.1017/jfm.2024.1008).
The experiments were conducted in a water channel at the Norwegian University of Science and Technology. The setup includes an active grid to control freestream conditions. To analyze the evolution of the flow, the boundary layer was tested at four different streamwise locations for three grid sequences with freestream turbulence intensities up to 10.9%. Careful preprocessing was implemented to ensure high accuracy and minimal uncertainties.
This work was funded by the Research Council of Norway (see funding information): Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the Research Council of Norway. The granting authority cannot be held responsible for them.</p
Optimization of Pin-Fins for a Heat Exchanger by Entropy Generation Minimization and Constructal Law
No full textP.O. Box 552, Xi’an 710072, Shaanxi, China
Masoud Asadi
Department of Mechanical Engineering, Azad Islamic University Science and Research Branch, Tehran 1615918683, Iran e-mail: [email protected]
Giulio Lorenzini
Full Professor Department of Industrial Engineering, University of Parma, Parco Area delle Scienze, 181A, Parma 43124, Italy
1 Introduction
Employing pin-fins on a heated surface promotes heat transfer performance. Given their inexpensive and simple structure, pin- fins have extensive applications in cooling ranges from electronic equipment to the automobile industry. In diesel engines, about two-thirds of the input energy is wasted through the exhaust gas and cooling water. In this sense, it is important that a serious effort should be launched for conserving this energy. A pin-fin heat exchanger is an excellent choice for recovering waste energy in an automobile with diesel engine. Traditional methods for design- ing the exchanger are not very applicable because of relatively high pressure drop. Effective optimization methods are therefore necessary to enhance heat transfer performance with low pressure drop. Although there exist various methods for optimization of designs of heat exchangers, such optimizations were considered as manual designs by using different optimization algorithm rather than based on nature design from the standpoint of thermodynam- ics. This study focuses on the optimization of pin-fin geometry for a new heat exchanger by using EGM and CL.
EGM is widely used to evaluate thermal and energy systems in view of thermodynamic imperfection [1,2]. For example, Saffari- pour and Culham [3] presented a new nonintrusive method for the measurement of entropy production in microscale thermal-fluid devices. The entropy generation map was also obtained by post- processing the velocity and temperature distribution data. They used microparticle image velocimetry and laser-induced fluores- cence methods to measure data. Li and Kleinstreuer [4] analyzed the entropy generation in trapezoidal microchannels. They found that there existed an optimal Reynolds number range in order to
1Corresponding author.
Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 22, 2014; final manuscript received June 25, 2014; published online March 17, 2015. Assoc. Editor: Cesare Biserni.
Optimization of Pin-Fins for a Heat Exchanger by Entropy Generation Minimization and Constructal Law
Pin-fins are considered as one of the best elements for heat transfer enhancement in heat exchangers. In this study, the topology of pin-fins (length, diameter, and shape) is opti- mized based on the entropy generation minimization (EGM) theory coupled with the con- structal law (CL). Such pin-fins are employed in a heat exchanger in a sensible thermal energy storage (TES) system so as to enhance the rate of heat transfer. First, the EGM method is used to obtain the optimal length of pin-fins, and then the CL is applied to get the optimal diameter and shape of pin-fins. Reliable computational fluid dynamics (CFD) simulations of various constructal pin-fin models are performed, and detailed flow and heat transfer characteristics are presented. The results show that by using the proposed system with optimized pin-fin heat exchanger the stored thermal energy can be increased by 10.2%
Publisher Correction: Multi-step ahead forecasting of electrical conductivity in rivers by using a hybrid Convolutional Neural Network-Long Short-Term Memory (CNN-LSTM) model enhanced by Boruta-XGBoost feature selection algorithm
No full textCorrection to: Scientific Reportshttps://doi.org/10.1038/s41598-024-65837-0, published online 01 July 2024 In the original version of this Article, Changhyun Jun and Aitazaz Ahsan Farooque were omitted as corresponding authors. The correct corresponding authors for this Article are Masoud Karbasi, Changhyun Jun and Aitazaz Ahsan Farooque. The original Article has been corrected. © The Author(s) 2024
Vascular Vertigo
No full textVertigo is a common complaint in neurology and medicine. The most common causes of vertigo are benign paroxysmal positional vertigo, vestibular neuritis, Meniere’s disease, and vascular disorders. Vertigo of vascular origin is usually limited to migraine, transient ischemic attacks, and ischemic or hemorrhagic stroke. Vascular causes lead to various central or peripheral vestibular syndromes with vertigo. This review provides an overview of epidemiology and clinical syndromes of vascular vertigo.Vertigo is an illusion of movement caused by asymmetrical involvement of the vestibular system by various causes. Migraine is the most frequent vascular disorder that causes vertigo in all age groups. Vertigo may occur in up to 25% of patients with migraine. The lifetime prevalence of migrainous vertigo is almost 1%. Cerebrovascular disorders are estimated to account for 3% to 7% of patients with vertigo. Vestibular paroxysmia has been diagnosed in 1.8% to 4% of cases in various dizziness units. Vasculitic disorders are rare in the general population, but vertigo may be seen in almost up to 50% of patients with different vasculitic syndromes.Conclusions: Migraine, cerebrovascular disorders especially involving the vertebrobasilar territory, cardiocirculatory diseases, neurovascular compression of the eighth nerve, and vasculitis are vascular causes of vertigo syndromes. </jats:p
Consolidation characteristics of soft sediments by seepage induced consolidation test
No full textThe thesis presented herein outlines the seepage-induced consolidation test (SICT) results of soft sediments dredged from Newark bay, NJ, for the determination of consolidation characteristics. The Seepage induced consolidation testing device was constructed based on the original version (SICT) presented by Dr. Prof. Dobroslav Znidarcic at the University of Colorado Boulder (CU). The author traveled to CU and consulted Dr. Znidarcic for recommendations on the device design and construction, preferred manufacturers, and sample testing procedures. A SICT device was then designed and constructed for Rutgers University in New Brunswick, with some modifications like deadweight loading system for easier troubleshooting. The SICT results for kaolinite clay, performed by Dr. Znidarcic at the CU laboratory, were compared with the author's test results from the Rutgers Soil and Soft Sediment Laboratory. The comparison served to assess the reliability and repeatability of the Rutgers University SICT device. Following the collection of dredged sediment samples from the Newark bay area, five different clays were purchased and their consolidation characteristics were tested. In addition, the tests sought to determine a correlation between sediment index properties and consolidation model parameters. Index property determination is less time consuming and cumbersome than consolidation testing under seepage force, which is more technical and can take up to two weeks for a single test. Therefore, there is inherent merit in gaining insight into consolidation behavior without running the seepage tests. A total of sixteen tests were performed. Eleven tests were conducted on the Newark soft sediments, and the remaining five on the clay samples. The results have been partially published via the 15th Asian Regional Conference in Japan, the International Conference on Civil Engineering in Iran, and the Journal of Geotechnical Engineering. The consolidation model parameters were correlated with the samples' index properties and the resulting equations satisfactorily approximated the reality.Ph.D.Includes bibliographical referencesby Masoud Janba
Importance Sampling for a Markov Modulated Queuing Network with Customer Impatience until the End of Service
No full textFor more than two decades, there has been a growing of interest in fast simulation techniques for estimating probabilities of rare events in queuing networks. Importance sampling is a variance reduction method for simulating rare events. The present paper carries out strict deadlines to the paper by Dupuis et al for a two node tandem network with feedback whose arrival and service rates are modulated by an exogenous finite state Markov process. We derive a closed form solution for the probability of missing deadlines. Then we have employed the results to an importance sampling technique to estimate the probability of total population overflow which is a rare event. We have also shown that the probability of this rare event may be affected by various deadline values.Importance Sampling, Queuing Network, Rare Event, Markov Process, Deadline
Vibration of Bundled Conductors Following Ice Shedding
No full textThe dynamic behavior of bundled conductors following ice shedding from one subconductor is examined numerically using the finite-element method. An existing model of ice shedding from a single conductor is improved by developing a model of spacers which connect subconductors in the span. The resulting system makes it possible to simulate vibrations following ice shedding from one span of an overhead transmission line with twin, triple, or quad bundles. Vibration characteristics are evaluated as the following parameters are varied: thickness of shed ice, distance between adjacent spacers, and number of subconductors in the bundle. Simulation results will provide information on how the amplitude of vibration and the transient dynamic forces change with the application of spacers. The maximum jump height of the ice-shedding cable, the maximum drop of the loaded cable, and the maximum cable tension are approximated as power functions of ice thickness and the distance between adjacent spacers
Exploring potential serum levels of Homocysteine, interleukin‐1 beta, and apolipoprotein B 48 as new biomarkers for patients with ischemic stroke
No full textBackground: Stroke is the second leading cause of death worldwide with heterogeneous characteristics. The subtypes of stroke are due to different pathophysiological regulations and causes. This study aimed to investigate the correlation of serum levels of apolipoprotein B 48, interleukin-1 beta and Homocysteine with BMI in patients with ischemic stroke (IS). Methods: Over one hundred controls (120) and an equal number of IS patients, including 31 women and 89 men, were recruited to participate in the case-control study conducted at Imam Reza Hospital (Tabriz, Iran) from February 2019 to March 2020. We measured serum levels of apolipoprotein B 48, interleukin-1 beta, and Homocysteine. Receiver operating characteristic analysis (ROC) was performed to evaluate the diagnostic value of these indices in patients and control groups. Results: The mean serum levels of apolipoprotein B 48, interleukin-1 beta, and Homocysteine, were significantly increased in the experimental group compared to the control group with a p-value of 0.001. The ROC curve analysis showed that the area under the curve for apo B48, IL-1 beta, hs-CRP, and Homocysteine serum levels were 0.94, 0.98, 0.99, and 1, respectively. Conclusions: The results of our current study show that the determination of serum levels of apolipoprotein B 48, interleukin-1 beta, and Homocysteine can potentially be used to monitor and diagnose IS patients. However, there was no statistically significant correlation between serum levels of apolipoprotein B 48, interleukin 1 beta and Homocysteine and BMI in the patient group. However, there was a statistically significant inverse correlation between serum levels of high-sensitivity C-reactive protein (hs-CRP) and BMI in the patient group.Research Vice-Chancellor of Tabriz University of medical sciences, Tabriz, IRAN [25992]The present study was supported by grants from the Research Vice-Chancellor of Tabriz University of medical sciences, Tabriz, IRAN grant no. 25992
Efficient Massive Machine Type Communication (mMTC) via AMP
No full textWe propose efficient and low-complexity multiuser detection (MUD) algorithms for Gaussian multiple access channel (G-MAC) for short-packet transmission in massive machine type communications. To do so, we first formulate the G-MAC MUD problem as a sparse signal recovery problem and obtain the exact and approximate joint prior distribution of the sparse vector to be recovered. Then, we employ the Bayesian approximate message passing (AMP) algorithms with the optimal separable and non-separable minimum mean squared error (MMSE) denoisers for soft decoding of the sparse vector. The effectiveness of the proposed MUD algorithms for a large number of devices is supported by simulation results. For packets of 8 information bits, while the state-of-the-art AMP with soft-threshold denoising achieves 8/100 of the upper bound at Eb/N0 = 4 dB, the proposed algorithms reach 4/7 and 1/2 of the upper bound.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Signal Processing System
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