Standard errors estimation in the presence of high leverage point and heteroscedastic errors in multiple linear regression

In this study, the Robust Heteroscedastic Consistent Covariance Matrix (RHCCM) was proposed in order to estimate standard errors of regression coefficients in the presence of high leverage points and heteroscedastic errors in multiple linear regression. Robust Heteroscedastic Consistent Covariance Matrix (RHCCM) is the combination of a robust method and Heteroscedasticit Consistent Covariance Matrix (HCCM). The robust method is used to eliminate the effect of high leverage points while HCCM is mainly used to eliminate the effect of heteroscedastic errors. The performance of RHCCM was assessed through an empirical study and compared with results obtained when the original Heteroscedastic Consistent Covariance Matrix was used

Multi-layer micro channels system: interpretation and developments

During the last three decades the concept of the traditional cooling systems was modified to include single, double, and multi-layer micro channels. The new studies, applications, fabrication, and research focus on four main areas: the geometrical shape of the micro channels, the number of stacked layers, the type of the coolants, and the heat performance optimization. The previous studies have shown a significant reduction in the power consumption as the optimization is accomplished. In this paper, a semi-review for the previous works is provided, an attempt to interpret the nature of the work done, and show another trial for optimization. In this study, water was used as a coolant agent, stacked multi-channel was adopted, and thermal resistance network was calculated.The heat sink under consideration is a rectangle of width ?? and length ??. The thickness ???????? of the base of the micro-channel is 100 [?m] while the depth ????of the micro-channel is 500[?m], both kept constant for all future optimization cases

Optimization of multilayer micro channels heat sinks cooling system using genetic algorithm

Cooling of electronic devices is problematic by its nature simply because of the space restriction. Recent advances in high powered miniaturized electronic systems have come at the expanse of very high heat fluxes that pose challenges to thermal management research. Uncontrolled excessive heat may cause thermal fatigue and stresses and the current micro electro-mechanical cooling systems (MEMS) which utilize the single layer micro channel heat sink, introduced a decade ago, may no longer be an adequate solution. Possible extension of the layer of parallel micro channels into a stacked system, by developing two, three, and multi-layer channel systems are being investigated. The design of all these systems depends on several parameters; coolant type, channel geometry, channel dimensions, and the number of the channels. This paper reports a new model for optimizing the thermal resistance, developed based on specific parameters of the dimensions of the channel, the wall width between the channels, and using water as a coolant at 27°C. The outcomes of the model were compared with other published studies. The results showed that the model is valid and reliable for further studies

Single-objective optimization of a thermoacoustic refrigerator

Optimization of energy-related systems with by-products that involve environmental degradation has never been so crucial today with depleting resources and global concerns over negative impacts on our environment. This paper reports the results of an optimization scheme on the coefficient of performance (COP) of a standing wave thermoacoustic refrigerator based on genetic algorithm. The environmentally friendly refrigerator operates without any CFCs, which has been associated with the depletion of ozone, a substance that prevents uv light from reaching the earth’s atmosphere. A single- objective optimization to maximize the COP of a thermoacoustic refrigerator has been completed. The variables investigated include the length of the stack, Lsn, center position of the stack, xsn, blockage ratio, B and drive ratio, DR. The results show that a COP of up to 1.64 is achievable which provides promise for future improvements in the present systems

Pembentukan nilai dan kecemerlangan bagi melahirkan generasi muda yang mapan dalam menghadapi era pasca modenisme

Dalam era Pasca Modenisme, generasi muda perlu diberikan perhatian khusus kerana mereka merupakan golongan paling dominan untuk diletakkan pelbagai harapan dan hala tuju agama, bangsa dan negara. Golongan ini merupakan pewaris kepada kepimpinan dan kehidupan akan dating. Justeru itu, keperibadian mereka harus dilentur sedaya mungkin agar keseimbangan rohani, intelek, emosi dan jasmani terbena dengan suburnya. Ciri-ciri pemuda cemerlang mengikut kajian sarjana Islam dan Barat cuba diketengahkan untuk dijadikan ukuran dalam menentukan hala tuju generasi muda dewasa kini. Ciri-ciri pemuda cemerlang yang dikemukakan ini merupakan pilihan daripada banyak teori-teori kecemerlangan pemuda yang lain. Kemahiran-kemahiran yang menjadikan seseorang pemuda cemerlang juga akan diketengahkan. Ini termasuk aspek kerohanian, pengurusan diri, bersosial, berorganisasi, kepimpinan, berkomunikasi dan berdakwah. Kemahiran ini perlu dikuasai bagi memastikan ia mempunyai persedian yang mapan untuk melayari bahtera kehidupan sebagai seorang pemuda yang berwawasan. Apabila pemuda kita bangkit dengan segala penampilan yang sempurna, penuh keyakinan, keilmuan dan keterampilan yang mantap, satu revolusi pemangkin ummah akan dapat dijelmakan. Pemangkin ummah yang mempunyai kekuatan dari aspek keperluan kehidupan duniawi dan ukhrawi seterusnya mampu menangani segala permasalahan yang mendatang dalam Era Pasca Moden ini

Effects of two-phase flow friction factor correlations on the optimal pressure drop-martinelli parameter pair in a mini-channel

Substantial research has been completed with more on-going on the flow pattern and heat transfer associated with two-phase flows. Discrepancies reported may have been as much as agreements, due to the different models, approaches, flow regimes, correlations, and new working fluids being utilized. This paper reports the outcome of a study to look at the effects of applying two different friction factor correlations on the simultaneous minimization of the pressure drop and Martinelli parameter under optimized flow rate and vapor quality, using genetic algorithm. The homogeneous model is assumed with ammonia as the working fluid, the coolant being environmentally friendly and having recently discovered as a potential replacement for the current refrigerants in micro and mini-channels. Results show that significant differences in the frictional pressure drop and Martinelli parameter arise due to the different correlations used, and this is only the outcome from two different correlations currently being considered by researchers in pressure drop analysis for two-phase flows in mini-channels. Thus, absolute agreement is indeed not possible between theoretical, experimental, and numerical work in view of the many different available correlations being utilized today with differences between 10 to 100 percent that has already been established

Extreme learning machine based sub-key generation for cryptography system

The key generation process is the substantial step in any cryptosystem. Incorporating Artificial Neural Network (ANN) in the algorithmic work of cryptography achieves good performance in realizing high accuracy and security. In this paper, ANN based sub-key generation algorithm is presented. Extreme learning Machine (ELM) type is adopted for one hidden layer neural network. Initial key includes all needed information about ANN topology, activation function, and seeds for Pseudo-Random Number Generation (PRNG) in each round to initialize input-hidden layer weights and data. Sub-key in each round is generated from output layer weights. Evaluation measures have proved complete sensitivity and inevitability of this approach. In addition, it contributes in reducing the risks of breaking the symmetric key algorithms due to the generated independent sub-key in each round. Thus, it can be integrated in any cryptosystem for subkey generation

Characteristics of two-phase flow heat transfer of R-22 and R-290 in horizontal circular small tube

Hydrocarbon refrigerants have been widely used to replace HFCs. As hydrocarbon, R- 290 has no ODP (Ozone Depletion Potential) and negligible GWP (Global Warming Potential). This paper presents flow boiling heat transfer in small tube with R-290 and R-22. The test tube has inner diameter of 7.6 mm and length of 1.07 m. In order to determine the heat transfer coefficient, experiments were carried out for heat fluxes ranging from 10 to 25 kW/m2K, mass fluxes ranging from 204 to 628 kg/m2s, and saturation temperatures ranging from 1.87 to 11.9o C. The study analyzed the heat transfer through the local heat transfer coefficient along the flow under the variation of these different parameters. In comparison with R-22, R-290 provides higher heat transfer coefficients. In the prediction of the heat transfer coefficients of R-22 and R-290, the correlation of Shah (1982) and Choi et.al. (2009) best fitted the present experimental result, respectively

Optimal frictional pressure drop and vapor quality relationship of ammonia and R22 in two-phase flow

Research in two-phase flow in heat exchanging devices plays an important part in today’s applications in miniaturization of engineering systems. The phase change process factors in the flow conditions and heat transfer in evaporators and condensers. Numerous studies in the past have looked at the predicted and measured frictional pressure drop of coolants as the vapor quality increases. This paper reports a preliminary attempt at modeling of the relationship between the frictional pressure drop and vapor quality in an ammonia-cooled and R22-cooled mini-channel of 1.5 mm diameter under optimized conditions using multi-objective genetic algorithm. R22 is a being phased-out due to its ozone-depleting characteristic and ammonia is being considered as its potential replacement. The properties of ammonia and R22 used have been obtained experimentally at the saturation temperature of 5?C and 10?C respectively. Modeling of the minimized pressure drop per unit tube length together with the Lockhart-Martinelli parameter was completed under optimized flow rate and vapor quality.The outcomes obtained are similar to those that have been reported experimentally with other coolants, increasing pressure drop with increasing vapor quality

GREEN SYNTHESIS NANOPARTIKEL GRAPHENE DENGAN AGEN PEREDUKSI URIN MANUSIA DAN APLIKASINYA SEBAGAI ADITIF BIONANOLUBRICANT BERBASIS CPO (CRUDE PALM OIL)

Graphene is a nanomaterial that has been widely applied to various fields because of the uniqueness of the material, therefore this material is very interesting to be developed as an additive in lubricant. This study aims to determine the optimum additive weight ratio and obtain optimum operating conditions in the graphene dispersion process in base oil. This research is divided into 2 stages: preliminary research and main research. The preliminary study aims to transform the chemical structure of crude palm oil (CPO) through a three-stage reaction into a polyol as a base oil. The main research is the process of making bionanolubricant. Graphene is synthesized using a combination technique with a human urine as reducing agent. The formulations are known by varying the weight of the additive and the time of the dispersion. Variation of additive weight was 0% (A1), 0.25% (B1), 0.5% (C1), 1% (D1) while for dispersion time variation ranged from 0 min (A2), 60 min (B2), 90 minutes (C2) and, 120 minutes (D2). Based on the SEM-EDX test results, the SEM image formed graphene and spectrum layers on EDX show that the oxide in graphene has been successfully reduced. Bionanolubricant was tested for quality with 7 parameters. The composition of base oil formula 250 gr and graphene nanoparticles 0.5% w / w is the optimum additive weight ratio for C1 sample code whereas the economical dispersion time is 60 minutes. The result of the viscosity index test is 121,72, its pour point is 10,4oC, flash point equal to 228oC with lubrication capability tested through four ball tester got scar diameter equal to 0,87 mm. This Bionanolubricant belongs to the SAE 250 class and is classified as a GL-4 lubricant based on the quality level of API (American Petroleum Institute) performance test